What all do you consider “synchronizing” to include? I mean, the calendars won’t, but using Etar+NextCloud for calendar, and Tuta for email, has worked fine for me. Of course it means that my calendar isn’t encrypted.
I just tested sending an ICS event to both. The Tuta app offered to open it on Etar, and Etar offered the default calendar with dropdown for others, just like normal. (Strangely it didn’t even offer to open on Tuta’s own calendar, which is in the same app; maybe because I’ve added no calendars there?) Proton’s app (which may be out of date, the mail app isn’t on F-droid, either publicly or in an official repository, and I’m a lazy updater) wanted to open it on Proton Calendar only when I don’t even have it installed.
Proton’s bridge OTOH worked really well for me for syncing to Thunderbird, probably works as well for Office too.
Depends a lot on your peer group, but I have even fewer contacts that use PGP than ones that use either service. :/ Just tried to keep it simple.