Hi @mreitschuster,
I have never used and seen this function in a manual installation … maybe this is due to your container.
In the config.php file you can disable the check for updates but it will only bypass the problem …
just add :
'updatechecker' => false,
maybe by reading the file config.sample.php you will find something interesting (this file lists all the possible parameters on your nextcloud instances, for them to be taken into account please add them in config.php)