Just so I don't misunderstand, does that mean I need XDR or will it work with any monitor? I was very surprised to see that the original M1 only supported one external monitor so just want to confirm before I press buy.
No it will, it's just a very demanding monitor so if it can run multiple of those it will have no problem with random 1080p or 4K monitors.
It will of course work with other monitors, but there aren't that many high res monitors out there. The Apple display is the only 6k monitor I know of. There are a few 5k monitors and lots of 4k monitors.
There's one 8k monitor from Dell, but I don't think it's supported by macOS yet.
It's their marketing term for their HDR tech. The XDR displays are their flagship media productivity monitors. The new screens in the 14/16 inch MacBooks have "XDR" tech as well.