Using New Outlook on Windows for personal email, calendar, and contact management
Betterbird is well-maintained. Especially the recurrent amnesia of Thunderbird with login credentials has been solved.
The Thunderbird team is unresponsive.
I have not experienced crashes on Win11 and the app is lightning fast with 160k emails. I use Gmail, Outlook, Gmx, Yahoo and other providers and it all works well.
With Thunderbird there were random issues and frustrations.
These guys took the Thunderbird codebase and fixed and improved it. Email has just become an app that I use but never notice, because it works ...