The Nextcloud App Store has a wide variety of apps that can be installed on top of Nextcloud. Nextcloud has no native sandboxing mechanism for plugins - if a plugin fails, it will bring down the whole installation. Plugins might also break an installation after a Nextcloud upgrade. For this reason, we encourage carefully reviewing apps before using them.

If it's not immediately obvious which plugin may be causing an issue, edit /app/data/config/config.php and set debug to true. Save the file and refresh the browser (do not restart the app because restarting it will reset the debug value back to false). It will then contain a stack trace of the error which should help identify the plugin.

Once identified, open a Web terminal. Then run the following commands:

sudo -u www-data php -f /app/code/occ app:list            # this lists the apps

sudo -u www-data php -f /app/code/occ app:disable <app>   # use this to disable the faulty app

After running the commands, end the repair for the app to come up.