There has been lots of studies done on Mid-Life Crisis; assuming it is Real it seems to involve Genetic, Biological, Psychological and Social factors. So you have to consider each one in turn, interpret it in your specific context and then take action.

Here are some resources that you may find helpful:

1) https://en.wikipedia.org/wiki/Midlife_crisis

2) https://www.nature.com/articles/s42003-021-02206-x

3) https://www.theatlantic.com/magazine/archive/2014/12/the-rea...

4) https://openthemagazine.com/science/the-genetic-origins-of-a...

5) https://www.fatherly.com/health-science/am-i-having-a-midlif...

6) There is a tradition of "mind training" in Tibetan Buddhism called Lojong (https://en.wikipedia.org/wiki/Lojong) which you may want to study, learn from and put into practice. These are basically a set of practical advice/sayings/aphorisms/proverbs/etc. which teach you how to develop/modify your attitudes and perceptions towards life/other people/yourself in general. It was developed in the context of Buddhist practice but you can easily transfer the principles outside of it. A good starting point is the book Essential Mind Training: Tibetan Wisdom for Daily Life translated by Thupten Jinpa.