Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
This is already a thing and has been for years. Just go to your display settings and extend or duplicate it to the ipad. You can hide any and all ipad UI at that point and use it as a purely external screen over USB C or wirelessly

I hooked M4 IPP to my G32P via USB-C just for fun last year . . . everything was . . . comically large.

USB-C -> HDMI connecting the same IPP to the 80" displays in the school generated a lot of student attention 🙂
 
That was the first thing I checked besides now you can set the resolution, plus the touching, but unfortunately, nope…still landscape.
Ugh! Thanks. You just saved me the trouble of loading iPadOS 27 Beta. I bought a portable monitor because of this. Maybe next year.
 
Very nice advancement. Now the fidgetty build your own PowerBook with touch may revel on this. My idea: an MacOS/AppleOS iPad with folio keyboard/magic keyboard.

And a 5G MacBook Ultra with 4k 120 Hz screen and a avatar/gif apple logo/outside touch and notes input screen on the back. Killer premium series!
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.