I have had issues with nextcloud breaking randomly every time ive tried it. The thing I wanted the most was the caldav/webdav to integrate with Gnome and Davx5 (and finally kill google calender), and to get that I tried Owncloud instead. The UI leaves a lot to be desired but if you only use the *dav functionality it works like a charm. It also has a mobile app for syncing and several extensions but I havent delved into them.