I have experienced freezes shortly after running dnf on one of my machines. It has nothing to do with GNOME, it happens even in runlevel 3 (multi-user). I found this bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1826091
It claims the problem is fixed with kernel 5.6.7 which is in testing, I haven't tried it yet.
https://bodhi.fedoraproject.org/updates/FEDORA-2020-21c51fd821
Fortunately, despite it happening shortly after a dnf transaction, I haven't seen any signs of the transaction being corrupted. AFAICT everything in the transaction is written to disk before the freeze, even though other file system changes (such as bash history) often aren't.