I just updated my system via
dnf update, and after a reboot, my external
screen was extremly laggy (like 1 second lag). After some debugging, trying
the binary nvidia driver (couldn't get the display to work after all), I
dnf updated. Executed
dnf history, searched for the
update command, and executed
dnf history info 57 (where 57 is the transaction id).
It showed an update of the X server, which I suspected caused the lag.
I listed the old versions with
dnf --showduplicates list xorg-x11-server-Xorg and
dnf --showduplicates list xorg-x11-server-common and downgraded them to the second
last version with
dnf install xorg-x11-server-Xorg-1.20.5-7.fc31.x86_64 xorg-x11-server-common-1.20.5-7.fc31.x86_64.
After a reboot, the lag is gone. Maybe this helps someone. I just hate the Linux graphics subsystem :(