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: