I think that the key point here might be the curved part. Curved ultrawides mostly took over the market for large monitors cause they offered better ergonomics (curved + horizontal only head movement) and enough real estate.

Many places you can search for but whatever works for you. One quick example: https://www.dell.com/en-us/lp/best-monitor-size-for-gaming

I'm really not sure what Dell (or whoever else is pushing this) is trying to accomplish. A standard 32" 4K monitor exceeds retina requirements at 2ft!

At 5 feet most folks won't be able to tell the difference between that 4K monitor and a 1080p panel the same size - and could save themselves a lot of money + GPU power by opting for the 1080p.

If 2ft from a 40" monitor is fine for your neck, again, glad it works for you. But ergonomics is about avoiding strain and injuries not the minimum your retina needs to distinguish letters on a screen.

The 2ft was in reference to the 32" monitor Dell's advice references. I sit roughly 3ft 6in away from the screen in my desk setup - which per a Television-oriented calculator is about optimal for a 40" panel.

I'm honestly not sure why PC-oriented calculators are so much more conservative about field-of-view than THX is.

Probably because with PCs you typically want to be able to focus on any particular part of the screen without moving your head a lot while with a tv relying on more peripheral vision is normal and expected.

I don't know much about monitor ergonomics. Is the principle here that it is better not to move your head?

I don't understand; if the market exists, then why can't you find any?

To be clear, I can find plenty of widescreen displays in this category - it's the 16:9 aspect ratio that seems to have dissappeared. Adn if needs be I'll probably make do with a widescreen monitor, but as most of the content I consume is optimised for 16:9, the edges feel like a bit of a waste (and the center is over-dense PPI if you opt for the full 2160 vertical resolution on these displays)