By the specs, the #Librem5 screen is a little higher res than the standard iPad. So, still quite nice.
I’ve had both 720p and 1080p phones. I won’t say I can’t tell the difference (with reading glasses on), but as @todd said, it’s definitely an area of diminishing returns beyond 720p.
Also, you can still watch 1080p videos on a 720p device, and the quality will be higher than a 720p video because of fewer compression losses. I do that kind of thing all the time, even 4K on a 1080 monitor.