Suddenly, I cannot boot into Silverblue:
Entering emergency mode.
I attach a screenshot but cannot find the button to upload the rdsosreport.txt (should this be submitted to bugzilla?).
Prior to the failure I removed a nonexisting swap partition by
rpm-ostree kargs --editor and no more, see Looking for non-existing swap partition during startup: A startjob is running I was then able to boot into Silverblue. The boot failure occured after a system update, I believe.