what does "Read only Mode" as Heading on almost every Page in the Controlpanel mean, where could it come from? The Page below is empty.

I have that suddenly after working with Pages (creating, paste Markdown, reordering etc.), did not do anything else the last Days.

All Directories and Files in site/content/pages have chmod 777

The Debug-Bar shows that Actions Clear Cache / Stache etc. are running succesful.

Tried to switch PHP-Version from 7.3.16 (which is listed as "actual stable" and "recommended") to 7.4.4 (listed only as "new"). No Changes visible, so i changed it back to the running 7.3.16.

Log-Files are empty