Desktop app on iMac is not accessible

My iMac confirms that the desktop client has been installed properly and I can see it in Programms. But when trying to open it ( via launchpad, dock, finder …) I do not get any screen or menu.
Also the installation did not show any Nextcloud screen or menu.

Help highly appreciated!

I am an absolute beginner in these cloud, client, network issues.
Latest MacOS (14.0, Sonoma) is installed

Best,
Matthias

The same situation …
Sonoma 14.1.2
Click the app - nothing shows up anywhere.
Delete - Reinstall doesn’t help