Based on conversations with millennial-aged people (age 30 - 44 or so), things are not the same as they were in the early 2000s. I will write my own experience below. I am in one of the more conservative congregations (one of the most, actually), although like any other conservative Anabaptists, that means they just don't change quite as quickly to conform to the overall group norms. One of the "transitions" my congregation is currently going through is transitioning from having cheap, modest, and perhaps inadequate school buildings to having more expensive new school buildings. Most other congregations already made that transition.
Beliefs and accepted practices have been carefully defined with little room left for doubt as to what is "right" or "wrong." These begin with an emphasis on being redeemed from sinfulness, which results in an emulation of Christlikeness, focused both on attitudes and outward expressions in appearance, family and community relationships, vocation, and possessions. The decisions reached on these matters at conferences are binding. Unheeded infractions usually result in discipline, particularly during the yearly revival meetings. This has forced a fairly standard outward conformity: men wear relatively plain dress and beards; they avoid wearing ties. Women also dress simply and wear black head coverings (either a small cap or a kerchief tied under the chin. These symbols continue to serve as powerful reminders of religious obligations of being a faithful Holdeman Mennonite. Deviations in appearance signal tendencies toward defection and are dealt with by peer pressures of fellow church members, family, ministers, deacons, and the visiting ministers during their revival meetings. Observers have noted that they have managed to retain one of the most carefully disciplined groups in this respect in North America.
There is more room for doubt about what is "right" or "wrong" and there is much emphasis on teaching the importance of listening to the Holy Spirit with regards to being convicted about what to do, mostly because there are so many new scenarios appearing each day. Should you listen to podcasts on your phone? What about using AI tools to generate images, since we don't use photography? We rely far more on individual discernment than was the case 20 years ago.
Conference decisions are binding, but drift (mostly via the smartphone) is clearly evident, particularly in the area of recorded acapella singing; technically, this is only to be used on WhatsApp in the same manner as one would call someone up to sing a song to them, as happened in the old days when you would call someone and sing them a song or leave a song on their answering machine. Realistically, some people collect large amounts of recordings on WhatsApp and listen to it much like a music player app. Those who do seem to display zero conviction that they shouldn't be doing this.
Men wear blue jeans and T-shirts. The general standard is T-shirts shouldn't have fashion brand names on them, but the name of an employer is OK. I have a collection of T-shirts from various employers and also from vendors, which seems to be OK, too. When my son turns 5, he won't really be wearing any T-shirts with writing on them, but before age 5 it's generally okay to have normal fashions for children. In this sense, Holdemans are somewhat similar to German Baptists, except Holdemans cut off the mainstream fashions for children at a younger age (around 5). Likewise, girls would be wearing normal attire for 1 or 2 year old, but by age 3 or 4 or so would stop wearing pants for toddler girls and switch to wearing handmade Holdeman style dresses.
Women wear handmade Holdeman style dresses, although the styles can change. Currently a baggy, loose style made from linen or wool or other "natural" fabrics is the most fashionable. There is also a style of wearing anything vintage, either an actual, real vintage dress from the 1950s sourced from a grandmother's closet, or else careful tailoring and sewing to copy the 1940s and 1950s styles. Most Holdeman women avoid wearing anything as short as was in style in the 40s/50s (knee length), though, preferring to be a few inches past the knee. My wife's nieces were a bit surprised when they saw their grandmother's wedding dress at their 50th wedding anniversary celebration.
Some women choose to buy storemade clothes but this is generally considered fringe / on the edge / perhaps not spiritual / also not fashionable. Very rarely someone will encounter a Holdeman woman who wears skirts and shirts. There is actually no church stance against doing this.
Holdeman men generally do not wear athletic pants without a good reason to do so (such as attending physical therapy, like I do), and particularly youth boys do not wear this to youth events. Instead, blue jeans are the standard. Shorts are never worn. Well, except underneath one's pants, I suppose. The colloquial term "shorts" in Holdeman circles refers to underthings.
To church services, it is customary to wear something other than blue jeans (black jeans are acceptable) and a button down long sleeve shirt. Women wear the same kind of dresses they do during the week, except long sleeved. Some women don't want to do so much sewing, or gain weight and don't want to sew a whole new wardrobe, etc. and will just don a sweater over their ordinary dresses. Some men like to wear a 2-piece suit. Some preachers wear a 2-piece suit to preach in, but some don't.
Nearly all Holdeman women wear a plain black cap, although there is no church standard requiring this. One woman who is a friend we appreciate wears what we call a "flap out", which looks very much like a typical Beachy group which would be wearing plain black veils. Of course, to Sunday services, a Russian (or Ukrainian, depending on your point of view) style kerchief is worn. In the mission field other styles are worn since in some cultures, wearing black things is associated with evil. In those places, blue is common.
Haiti has developed their own styles including their own standard style of veils. They also have their own standards for what kind of dresses, etc are acceptable. The Holdeman women there wear tighter clothes than would be commonplace in the rest of North America. People who move there permanently are generally expected to conform to the local styles as doing otherwise is an expression of pride. In Haiti it is also common for women to weave extensions into their hair, but some prefer to just wear an entire head wrap to avoid having to do that. In the rest of North America, women wouldn't wear extensions.
Erring members are warned. If this goes unheeded they are ultimately excommunicated and avoided (shunned) by fellow members. It is estimated that about 10-25 percent experience excommunication. The fact that about 75-80 percent "repent" and return and are re-accepted attests to the success of their socialization and the feared experience of avoidance. Most important decisions are made at the conclusion of yearly revival meetings after they have observed footwashing (symbolizing their revival meeting "cleansing"), communion, baptisms, re-acceptance of repentant excommunicants, and the calling and ordination of ministers and deacons as needed.
This is about right, percentage wise in my experience, although excommunication only seems to happen anymore for very obvious death sins, and takes a long time. An example would be obvious fornication, such as moving in with a boyfriend/girlfriend, or becoming obviously pregnant out of wedlock. Another is smoking / chewing / drinking (beyond a single drink, i.e. becoming intoxicated). (Oddly enough, occasional vaping does not result in summary excommunication, yet.) Getting married outside of the church also results in summary excommunication, much as it would in other conservative Anabaptist groups. Most people I have known who are excommunicated eventually return.
They have a tightly knit, closed system of church member control centered in their "true church" concept; an insistence on unity in doctrine and practice; unquestioned following of their ordained leaders; decision making relegated basically to the ordained men; and a rigid doctrine and practice of church discipline which is coupled with the threat of eternal penalty. Attendance at other churches and participation in intimate spiritual relationships with nonmembers are regarded as bordering on "spiritual adultery" or listening to "false prophets."
This has changed somewhat, in that it is fine if someone wants to visit other churches. It is not permitted to try to start encouraging other church members to check out other churches, and one will be spiritually counselled if one starts pushing ideas one hears at other places. For example, one family had the husband start to be influenced by Finny Kurvilla's group, and he started to think perhaps we should switch to whatever those early church views allegedly on salvation via baptismal regeneration, etc. - this was strongly discouraged. I regularly visit other Anabaptist groups and it isn't viewed as a problem. When I attend something like AIC, I usually see another Holdeman member or two there, although they're often surprised to see me there, which recalls the old joke about taking two Baptists with you when you go fishing.
Overall, most Holdemans just don't enjoy visiting other Anabaptist groups. If the church is less conservative, the lifelong Holdeman member finds the experience debilitating. For example, we attended some baptisms, and my wife was shocked at how little was demanded of the supplicants to give their testimony (called "salvation experience" in Holdeman parlance) before being baptized. When attending a more conservative church, Holdemans might find it a bit boring. For example, the church service might be in German. The singing is just melody, not 4 part. If attending an evangelical service, Holdemans find the whole experience jarring - they don't enjoy the "rock concert" style of worship, even if they might enjoy sneaking in listening to country-pop music now and then. They also don't enjoy not chatting with the other congregants for a half hour after the service and can find that a bit impersonal. The end result is that Holdemans simply aren't motivated to visit other types of churches.
Overall, the Holdeman church institution is surprisingly stable, but the smartphone is presenting a major challenge to that institution, much as is happening simultaneously to the Old Order Amish.