jtx Board, an Android app that supports VTODO and VJOURNAL without making major compromises. Synchronization is done over DAVx5 and Nextcloud already fully supports it (there is no web interface for VJOURNAL though). However, you can check it out here: https://jtx.techbee.at/
I just installed Davx5 and jtxBoard and davx5 is connected and synced with my Nextcloud but jtxBoard simply don’t load anything, no notes, no task and no journal
I even disconnected davx5 install jtxboard then reconnect my nextcloud without success
As far as I understand, currently there is no other way than manipulating the SQL database to enable VJOURNAL for an existing NC calendar, right? So using the method described by nfetisov:
I use jtx Board and support the initiative to be able to sync VJOURNAL entries over NC. At the moment, I’ll look for other ways to back up my journal entries so they don’t get lost when I lose or break my current mobile device.
As @just said, there are currently no efforts being made by the Nextcloud developers to implement this feature. So the only thing left is for a third party to provide an app or extension, which means you have to do it your self, or maybe you get lucky and someone else does it, and shares it with the community…
However, I’m not sure how easy it would be to implement this. It could as well be that it requires a bit more than just a “little” app.