Technically it’s 1280x800 which is 720p but slightly taller. While saying it has an 800p display would technically be correct it doesn’t provide context for the actual resolution of the display since it’s only half of the full description of the resolution and there’s no widely agreed upon “800p” resolution. 720p has a coded understanding for how sharp a display is among tech knowledgable people. 800p has no such history. So while saying the steam deck has a 720p display may not be technically correct its actually a much more useful descriptor as most people understand how sharp that display is going to be.

Technically this “1080p” display isn’t even 1080p. Its 1920x1200 but it has the same pixel density as a similarly sized 1080p 16:9 display. So we say 1080. 4k is also not 4000 pixels. Its 3840x2160