I work with my own Nextcloud Server and Nextcloud Talk. Now I install the App to my eOS Gigaset GS 290 about the e Appstore and I get no Notifications, when I get Messages.
MicroG is working well with Threema and Signal, there I get push Signals. But no Notification Sound over Nextcloud Talk…
notifications are working fine with Google Store app, downloaded with Aurora Store app (even if Talk app isn’t open)
no notification with the F-Droid version
I guess this is the same problem as for many apps (see FOSS telegram) : only apps from Google Store include the necessary code for notification (Google Play Services), it is not included in FOSS apps as it may “brake the law”