I used thunderbird as a mail client for a while but eventually just gave up and switched to the web UIs, it was simpler and good enough. I didn’t know the calendar was that good, I should give it a try, thanks. Are there any specific features or use cases that make it stand above other (mail) calendars?
IIRC the web app had some intrusive ads(hard to remove and taking a bug chunk of screen space), is the offline version any better?