I rather Apple unlock it for 4k displays… Its on “Default” or “Large Text” on 1080p displays as well, as far I know…. “More Space” is only available for 5k+ displays.
It works on 4k Displays, It works on both my LG Ultra HD 4k and my LG Ultrafine 5k. I think the only prerequisite is a USB C connection, which the LG Ultra HD 4k has. Which is great because it powers the iPad, and has USB type A ports on the back, so the iPad is able to read those. So my 512gb thumb drive and my Logitech receiver for my mouse and keyboard work perfectly with one simple USB C connection. I don't have to switch bluetooth connections with my mouse or keyboard, the USB Logitech connector is picked up perfectly by the iPad Pro. So I can swap out a MacBook Pro or iPad Pro (or Steam Deck!) use one USB C connection and everything is picked up.
Sadly the LG Ultrafine 5k, which Apple partnered with LG on, preforms horribly with the M1 iPad Pro in Stage Manager. It basically breaks Stage Manager to the point that it's unusable. Stage Manager runs on the LG Ultra HD 4k normally, no bugs at all. So I do not recommend the LG Ultrafine, the Ultra HD 4k Model: 27uk670 works great and I would recommend it if you want a 4k monitor for your iPad Pro.