Joplin is all about security so why isn't there a sync option for Proton Drive? Can someone out there please make that happen? Thanks!
You can use filesystem sync for this, by pointing Joplin to the folder managed by Proton Drive
I've been using the Proton family of applications for quite a few years and what I have found with Proton Drive is that it does not appear to be a transaction based system like Dropbox or others. Rather, it seems to be a place to store files you need to keep secure but won't be needing access to very often. Sort of like a bank safety deposit box instead of an ATM. As such, it has no need for super-fast access, something you would need for a decent Joplin sync target. I use it extensively for backups but wouldn't think of using it for syncing anything.