Exactly same here.
Server: Win11, 4k Display, 1.0.65
Viewer, Win10, Lenovo8 small tablet, 1200×800 native resolution. Detected as 1200×800
Viwer downloaded from app store just now.
Switching between portrait and ladscape mode didn’t help.
It seems like horizontal and vertical size has been swapped or something.
I draw a circle in paint what is an eclipse on tablet.
My wallpaper is rotated left, and distorted.