Text appears blank / empty in Collabora

Running Nextcloud and Collabora with docker on my own server.
The server has 8G ram and ample space and speed. I have everything running except this:

When I type in a document or sheet, the text does not appear.
Example in the image: I typed ‘hello’ in field C1, and as you can see it is in the ‘value’ but not actually visible in the sheet itself.

The same happens for documents.

What causes this and how can I fix it?

Hello @moreforth, welcome to the community of Nextcloud.

You started a topic in support category. Unfortunately you ignored the template and a lot of information to help you is missing. Please add all necessary information like Nextcloud version, webserver type and version, os version, related log file content. Use the support template.

Use search many topics have been discussed already! As the system seems to works and just the display is wrong this might be related to some dark theme issue like discussed here: Can't see PDF files - #3 by wwe

Regards,
wwe