Thanks for the tips with the Nextcloud App @petefoth and @Danceswithcats , it saved my day ! I’ve struggling for a very long time with this issue…
I definitely thinks this should a matter addressed by the devs. It’s really weird that it is possible to setup very easily a lot of data from apps landed with the OS (like Address books, Calendar, Mail, Pictures and videos, etc.) and not the data from other apps also landed with the OS (like Music, or also Reccordings). As an experienced user, I find it very confusing.
Maybe a tutorial in the wiki would be a good start