Not a dev just a user, but I thought that it may be wise to let anyone who uses F-Droid know that they could be in for a bit of a surprise if they use additional repos and then accept F-Droid’s recommendation to upgrade Joplin.
As a result of this post it seems that there is an F-Droid repo out there that provides a download for Joplin. However the version provided is 1.0.337. This is a pre-release that upgrades the sync target. This means that if the update is processed no desktop clients can sync with the sync target unless they too are updated to a pre-release version (1.0.234+).(Release Notes). Furthermore, it seems that as there are currently no compatible releases for iOS or CLI, these versions would no longer be able to sync at all.
Just trying to prevent someone unnecessarily having a bad day …
It seems that there has been quite a bit of discussion on GitHub about this over the last few years.
Also from looking through that thread it seems likely that the Joplin apk came from the IzzyOnDroid Repo which the original poster had linked to their F-Droid app.