Nextcloud update fails (Web and CLI)

Hi there

If I use the Web-Interface updater, I get stuck at step 3.

So I SSHed into my installation and tried to run the installer via the CLI. This is what I got:

me@host /my_cloud/updater> php updater.phar
Nextcloud Updater - version: v20.0.0beta4-11-g68fa0d4

PHP Warning:  fopen(/home/httpd/vhosts/host/my_cloud/data/updater.log): Failed to open stream: No such file or directory in phar:///my_cloud/updater/updater.phar/lib/Updater.php on line 1110
Could not open updater.log
me@host /my_cloud/updater>

Nextcloud version: 21.0.7
PHP version: 8.0.23

Any ideas what could cause this problem?