I did open another console. I couldn't see anything obvious. What are the
tricks to finding a zombie process ?
I let dnf update complete and it did, successfully. When I rebooted the
main console wasn't completing to a login, so I knew something was up !
However I was able to get a login at a second console, so I did.
The graphical session never did boot for me, so I had no idea what login
was being used, so I tried a few things.
systemctl disable plymouth.service --force
systemctl disable graphical.target --force
systemctl disable lightdm.service --force
systemctl disable kdm.service --force
Then I did a bit of investigating
ls -l /etc/systemd/system/display-manager.service
This told me it was running sddm.
so: systemctl- disable sddm.service followed by shutdown -r now
Now it boots to a command line and runs at a reasonable speed !
I don't need a GUI right now anyway. I'll investigate further when I get
some time.