Settings → System → Display > Click Detect > Under “Multiple displays”:
Set to Show only on 1
NOT “Extend” or “Duplicate”
Then scroll and click:
Identify
Make sure only ONE screen is active.
Set Scale to 150% — that's the native recommended scaling for Surface Pro at its screen size and resolution. At 150% everything should look right.
Press Win + R → type regedit and hit the Enter key:
Delete these two keys:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\StuckRects3
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Streams
Reboot.