Honestly - the midlife WAS is almost always about THEIR issues, not ours. It seems odd, because surely many people leave their spouses for good reasons - but those spouses don't seem to end up here, doing the work, and their departing spouses wouldn't necessarily look like the ones we see here.
My ex had no legitimate reason to be dissatisfied with our life. He had a great job, we had a lovely house with an ocean view, no debt besides a moderate mortgage, 3 great if different kids, he had a loving wife, good sex life even after 26 years together. Nothing was perfect but life isn't perfect. His complaints about me really were just excuses to justify leaving. (How do I know that? Because one of his complaints was that I "walk too heavy" and that I had "taught our child to walk too heavy" lol. The more absurd the complaint, the more clear it is that this is about them, not you.
In retrospect, he had a pattern of dissatisfaction with other aspects of his life before he turned it on me. He was always looking for the next big thing to give him a "boost". I now see he's a narcissist too so any of our imperfections were intolerable to him because we didn't make him "look good".
Still - that being said - this process is an excellent opportunity to do self reflection, to make ourselves into a better version of who we are, to embrace change and even adventure in our lives. We ALL can become better and this crucible of change is a great place to do that.