Right-click the desktop
Open Display settings
Select the display you want to rotate
Find Display orientation
Choose Portrait
Click Apply
Confirm the change if prompted
On Windows, use Ctrl + Alt + Arrow keys if supported
On macOS, open System Settings
Go to Displays
Select the display
Choose Rotation
Set it to 90 degrees or 270 degrees
On Linux, open Display settings
Select the monitor
Set orientation to Portrait
Apply the changes