I am using joplin since long now, on two computers and one phone (Nextcloud/encrypted, Manjaro on the computers). It is fully operational and reliable.
I recently had problems with some notes remaining encrypted/unreadable.
A proposed solution on the forum is to follow the yellow bar's indication and retry unencryption. It is working but not all the time.
My understanding is that it is important also to work on the same (or nearly the same) version of Joplin on the computers to avoid major compatibility problem.
Manjaro does propose several options (AUR, Snap, AppImage..) with different versions; choosing the same version on the different workstations might be a good recommendation.
Working for me, I wanted to share!