On Gnome, relying on the little green app indicator icon is like relying on a house of cards. Gnome regularly changes its APIs which makes life hell for Gnome extension developers. The NC icon relies - I believe- on some legacy API thing and requires an extension. The NC app has had trouble reliably displaying the settings window under Gnome since it introduced that funny blue pop-up UI.
So now the nextcloud icon has gone again (Nextcloud app is running though, just invisible), I can debug Gnome, debug the AppIndicator and KStatusNotifierItem Support extension, debug the NC app, … or , I just wondered: is there a way to trigger the app to show the Settings window from the command line?
Because that would be a super helpful workaround for all the times one of these three moving parts makes it unusable.
What distro are you using? I have the AppIndicator and KStatusNotifierItem extension installed on both Arch and Fedora 36 (Gnome 42.4) and the status icon is working just fine. I’m using the Nextcloud Desktop Client from the respective repos of the distro.
But in order to try answer your question, I can also open the “funny blue pop-up UI” by typing nextcloud in the command line or by simply clicking on the icon in the GNOME app drawer. If you are using the AppImage, I guess you would have to execute the AppImage directly by typing /path/to/Nextcloud-3.6.0-x86_64.AppImage or double click it in the file manager. Btw. the AppImage does not provide an icon for the app drawer.
I’m not looking to open the blue UI, I’m looking to open the Settings UI. The blue one is a world of pain; yes it can be opened by restarting nextcloud, but unless your mouse happens to be over the spot where it opens, it immediately closes.
As for versions (which is all the stuff I was hoping to avoid as this is notoriosly deep) etc.
Runs Ubuntu 22.04, with Gnome shell 42.4, on Wayland, with app 3.6, and using the same extn as you, and using the NC AppImage, and yes there is an icon in the tray.
Runs Ubuntu 20.04 with gnome shell, v3.36.8 on Xorg, and the same extn installed: no icon. But others running the same do have it. I’ve tried running 3.6.0 and 3.4.x but neither shows its icon.