Mozilla is starting to throw resources at Thunderbird again, so it will hopefully get better this year. https://blog.mozilla.org/thunderbird/

Strange. I can't remember that last time it crashed on me, and I have it running almost all the time on my work and personal machines (both Win10, talking to gmail and fastmail respectively via imap).

A while back Mozilla announced that they were migrating development to an independent team. I don't know much about that, but my impression as a user is that quality hasn't been affected and it might even be getting more love. I was happy to donate some money to the project last time they did a fundraiser.