Nextcloud Office not working on shared host

I did a fresh install of NC 23 on my shared host with the latest versions of Collabora CODE and Collabora online. In the settings I see a green checkmark for the Collabora Server but when I try to open a document I get a download dialog. When I try to create a new document I get the message „Document could not be created from template.“ My share runs on PHP 8.0.21 with 1024MB memory. There are no errors in the Nextcloud log.

Then I switched to the Collabora demo server in Ireland and Nextcloud Office worked. I could open, edit and create documents. Any ideas what could be done to get Collabora CODE Server running?