I think it's really important to pay attention to the kind of writing - many things in Ecclesiastes aren't provably true if you try to interpret them that way. For instance, in the very next verse ...
There is no remembrance of former things,
nor will there be any remembrance
of later things yet to be
among those who come after.
Really? No remembrance at all? We certainly have histories and stories that have come down from the past, and Solomon certainly would have known that. Ironically, Solomon is well known even today. And he did something importantly new - he built the temple.
Yet in Ecclesiastes, Solomon tells us things that cannot be literally true - and he knows that they are not literally true. The whole theme of the book is that everything we do is smoke, transient, chasing after wind, and there is much suffering in life even if we do what is right, but the way of wisdom is to take joy in what God gives us, do what is right, and put our trust in what God does, accepting whatever life God gives us with joy.
Ecclesiastes 3 wrote:9 What gain has the worker from his toil? 10 I have seen the business that God has given to the children of man to be busy with. 11 He has made everything beautiful in its time. Also, he has put eternity into man's heart, yet so that he cannot find out what God has done from the beginning to the end. 12 I perceived that there is nothing better for them than to be joyful and to do good as long as they live; 13 also that everyone should eat and drink and take pleasure in all his toil—this is God's gift to man.
14 I perceived that whatever God does endures forever; nothing can be added to it, nor anything taken from it. God has done it, so that people fear before him. 15 That which is, already has been; that which is to be, already has been; and God seeks what has been driven away.
Ecclesiastes 4 wrote:18 Behold, what I have seen to be good and fitting is to eat and drink and find enjoyment in all the toil with which one toils under the sun the few days of his life that God has given him, for this is his lot. 19 Everyone also to whom God has given wealth and possessions and power to enjoy them, and to accept his lot and rejoice in his toil—this is the gift of God. 20 For he will not much remember the days of his life because God keeps him occupied with joy in his heart.
Our accomplishments are not what really matter, and most of us really will not be remembered three generations from now. But if you take some of his statements too literally, you miss the point. The temple Solomon built was indeed new, and it was significant, and it is still remembered. He wrote Ecclesiastes after this, yet he is saying that there is nothing new under the sun and all that we do is a chasing after wind. If you miss that contrast, you miss the heart of the book.
It's fascinating that the same Solomon who wrote Proverbs later wrote Ecclesiastes. Proverbs gives simple answers, Ecclesiastes tells us it isn't that simple. The Bible needs both books.
Is it biblical? Is it Christlike? Is it loving? Is it true? How can I find out?