@kevdog It is the Collabora Online App 3.6.0 Version, not the docker version. https://apps.nextcloud.com/apps/richdocuments
The solution is to set the following entry in Apache VirtualHost. https://nextcloud.com/de/collaboraonline/
# Endpoint with information about availability of various features
ProxyPass /hosting/capabilities https://127.0.0.1:9980/hosting/capabilities retry=0
ProxyPassReverse /hosting/capabilities https://127.0.0.1:9980/hosting/capabilities
This is how the Collabora Online Version 3.6.0 works.