PL, what method did you use to make the screen in Portrait mode?
What you pointed to in your pic in the Windows Display Settings.
You just need to turn your head and your mouse sideways

You used to be able to do this with previous version of Windows:
CTRL + ALT + Up Arrow changes to Landscape mode.
CTRL + ALT + Down Arrow changes to Landscape (Flipped) mode.
CTRL + ALT + Left Arrow changes to Portrait mode.
CTRL + ALT + Right Arrow changes to Portrait (Flipped) mode.