since i've read this community was created by mods of r/ProtonMail and chose to uncritically believe it, this is the closest we are to an officially lemmy presence, so...just to make sure this question is in every ProtonMail forum:
Exactly as stated, F-droid won't allow apps that use Google Play Services for their notifications. It's being worked on, but there's not ETA for that change. Not an easy one, I may add.
Believe me when I say, I'll be one of the first users jumping around like a kid on a Christmas morning when that happens. Not for F-droid itself (I prefer to download from GitHub with Obtanium) but to each one its own...
I've read somewhere that Proton Mail does not support notifications without Google Play Services... Not sure if F-Droid allows apps that use Google Play Services...
That would be lovely. There are few email clients available on fdroid and I've had issues with either anti features or getting the other ones to work with pop or IMAP.