The "free" version of outlook that replaced Mail is so bad that it made me finally switch to Thunderbird and I don't see myself going back anytime soon.
The only thing I'm missing sometimes is the Copilot integration, but copy and paste with Thunderbird is still faster than using Copilot in Outlook...
When I was using Thunderbird on Windows back years ago, i abandoned it in a week because it was absolutely slow when fed with years of archives as compared to Outlook 2010. Seeing recs for Thunderbird recently says something for sure.