In my case the /tmp/xauth-1002-_0 and /var/run/sddm/xauth_xpDgqp files
also have the same content. The ~/.Xauthority is different however.
Removing ~/.Xauthority does not appear to have any effect.
In my case I also have "ForwardX11 yes" in .ssh/config as I use X11
apps over ssh quite frequently. Removing that allows ssh to be quick
(as expected) although "su -" is still slow.
Note I am using X11 rather than Wayland.
When I downgrade to sddm-0.18.1-8.fc33 the "on-login" konsoles have
"XAUTHORITY=/home/terry/.Xauthority" and the R-click konsoles have
"XAUTHORITY=/tmp/xauth-1002-_0" and these two files are the same.