After the dist-upgrade to 20200823, my system did not log in to the graphical
environment (plasma). After reboot, it was worse.
The root fs was mounted read only and some services did not start because of
this.
After some poking, I decided to roll back. The system came up and I
dist-upgraded again. As Robert Munteanu hinted, there was a symlink from
/etc/systemd/system/tmp.mount to /usr/share/systemd/tmp.mount which I deleted.
The system rebooted normally this time.
I checked the snapshots and did not find this symlink in the rw snapshot after
the rollback, but in all previous until the one after the first upgrade to
20200823.
I did comment out the /tmp entry in /etc/fstab as described in the wiki to
migrate /tmp to tmpfs (https://en.opensuse.org/openSUSE:Tmp_on_tmpfs) and i
wrote a service to create a symlink from /tmp/dumps to /dev/null to prevent
steam from dumping gigabytes of logfiles there, effectively filling /tmp.