I cannot install the recommended apps

I have installed nextcloud as container/docker on my Qnap. When I start it now, I cannot install the recommended apps. After entering the user and password, the corresponding selection option is grayed out, a selection is not possible. How can I reactivate the app selection?
Alternatively, can I delete all accounts so that I can start all over again without the data hidden somewhere using my old profile again?

What about having a look into the adminstrator guide?
https://docs.nextcloud.com/server/latest/admin_manual/apps_management.html#apps-management

Thank you for your reply. Perhaps I didn’t make it clear enough. I have no way of accessing the app store at all. Clicking on the menu item does not lead to any reaction.
I have tried to uninstall and reinstall nextcloud, but I always get to the same point. I can’t open the appstore.
Could it be that Nectcloud is hiding a config file somewhere that is actually faulty and should be also deleted after uninstalling?

Can you install any app in the terminal by the occ command?

https://docs.nextcloud.com/server/stable/admin_manual/configuration_server/occ_command.html#apps-commands

In the provided admin guide parameters are listed which are used to enable/disable or customize the app store. Please double check the setting of these parameters and share the current settings with us.