Portrait mode on external monitor has wrong aspect ratio

jhuenem2 wrote:

Hi internet,

I have a 2013 MacBook Pro running Big Sur 11.6.2. I'm using an Asus VS197 as an external monitor with an HDMI > DVI cable connection.

I'm able to rotate the display of the external monitor 90 degrees, but the aspect ratio stays squished into 4:3-ish. How do I make the portrait mode actually be portrait mode?

I have done this once successfully, and haven't been able to recreate it.•

Things I have tried:

Holding the option key on the "scaled" option to look for extra resolutions (only offers 1024x768 or 800x600, when what I need is the opposite).

• Unplugging and replugging.

• Restarting.

What am I missing?

Did you try changing mirroring to native resolution or the opposite, to compare your results

Using a Retina display - Apple Support