problem solved
The following conf files of Webtop5 were available in /etc/httpd/conf.d/:
webtop5-webdav.conf webtop.conf
I removed them and let the httpd configuration update, then everything ran again.
Annoying such problems!
I had until 2 days ago both for testing installed, now only SOGO is installed.
When uninstalling, they were apparently not removed - that curious that as long as webtop5 was installed, there were no problems.