Are you sure it should be ?
.Xauthority is sorta legacy … modern sddm/kde creates the file dynamically…
something like /run/sddm/xauth_EWhnye
So … do you need a static one or a way to reliably find it for a reason?
If so there are ways to handle that …
https://wiki.archlinux.org/title/SDDM#X_authority_(aka_MIT-MAGIC-COOKIE)_file