When the graphical authentication prompt is displayed it follows the scaling of the primary monitor even if its displayed on another monitor with a different scaling factor.
In the attached screenshot I've triggered the prompt on my external monitor which is at 100% scaling. The primary monitor on my laptop is using 200% scaling.
ProblemType: Bug
DistroRelease: Ubuntu 23.04
Package: gnome-shell 44.0-2ubuntu3
ProcVersionSignature: Ubuntu 6.2.0-19.19-generic 6.2.6
Uname: Linux 6.2.0-19-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.26.0-0ubuntu2
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Tue Apr 11 11:13:36 2023
DisplayManager: gdm3
InstallationDate: Installed on 2023-04-05 (5 days ago)
InstallationMedia: Ubuntu 23.04 "Lunar Lobster" - Daily amd64 (20230404)
RelatedPackageVersions: mutter-common 44.0-2ubuntu3
SourcePackage: gnome-shell
UpgradeStatus: No upgrade log present (probably fresh install)
This is something that will fix automatically when you enable the "fractional scaling" even though you're not using fractional values, so I feel that's something that we won't change as upstream integer scaling is very likely being deprecated in non-x11.