I'm told it's this bug:
and it's related to haveing an old QtWebEngine + new glibc
I think the QtWebEngine package just needs to be updated, but I'll leave
it up to the experts.
I attached a screenshot showing the issue on a github page.
You can temporarily get around the issue with special launch options
(including not using your usual settings)
qutebrowser --temp-basedir --qt-flag disable-seccomp-filter-sandbox