Thank you for your answer! But this is not it. I have tried to disable and then removed the richdocumentscode app - it seems they were not active, since I switch off and removed the Collabora app 20 hours ago. Just to be sure I tried to disable and remove the app using occ. But it changed nothing.
Unfortunatelly there must be other app or process which tries to get fonts.json EVERY MINUTE. Any other ideas how to get rid of spamming my logs?
I have re-installed COLLABORA bulti-in server and Nextcloud Office, worked for a while and then de-installed. The problem described above reappeared. See the screen in the post above.
I decided to reboot the whole system. And it worked. The callings by COOLWSD HTTP Agent disappeared. This looks like a problem with PHP 8.1.2 or a cache …