I have a Dell 38" 21:9 and it’s great for desktop (non multimedia) usage.
I can have different screen setup but the one I use the most is my main window in the center, around 1900 px width, one at the left, around 1200, And there is still some space left on the right part of the screen, I use this space for a finder, sublime (notepad) or similar.
Before I had 2x22" monitor and this is a better setup.
I'm not against ultra-wide displays. I'll soon be purchasing at least one (maybe two) decent quality ultra-wide displays. But solely for running X-Plane flight simulator. For those who don't know, that's a genuine flight simulator and not a game. They'll work in conjunction with my 12.9" iPad Pro dedicated for mapping. And likely a Mac Studio computer (not sure which one, yet)
But... being a photographer who is pretty fussy processing my image files (check out my MR media content), I'll likely end up with Apple's new 5K display along with a Mac Studio. Having used a 5K iMac for around six years, I could never go back to anything less than a 5K display, and certainly not an ultra-wide.
The point of my post is, get the display that makes the most sense for your application and use.