Can I run ultrawide conveniently on a 16:9 Display?

With the rise of OLEDs where you are not bothered by backlight on black pixels, I wonder if I can run a "fake" ultrawide, non stretched, with 21:9 and black borders at top and bottom. Can this be done on win11 whithout third party? I'm asking because there's so much apps and games that just don't have support for ultrawide and this seems like a more suitable option for me