I just had another quick test of #ProtonCalendar .... I'm really happy to see the internal sharing capabilities coming in place.
The only truly missing feature now is basically a bridge solution so I can have my calendar in Thunderbird. Is such a bridge in your plans?
Also, how integrated is the calendar on #Anrdoid these days? I've not tested it this time, as last time it was completely unintegrated and was quite a hazzle to get other apps adding events to the calender. I can probably get used to using only the Proton Calendar app on Android - but an interface for other apps to add events is a must.
As this is progressing, I'm getting closer to replace #EteSync for calendars with Proton Calendar. But you're still not quite there yet, unfortunately.