To be fair there's a point here, which is that color spaces from sRGB to DCI-P3 to REC2020 do have quite different color/tone/brightness ranges (gamuts). Old windows boxes (and old monitors) also displayed them very differently (especially the low brightness ones). Macs were much better, and that made picking colors on them far more repeatable.

Now everyone in Windows world has standardized on sRGB and Mac on DCI-P3, but mobile is more important, where I believe it's still split sRGB Android, and DCI iPhone.

I don't know, but expect that HTML picked sRGB for their color space since this is the one people historically meant. I'd be surprised that it wasn't configurable and there weren't multiple versions, because why have a standard, when you can choose!

We won't even get into HDR, automatic brightness/eye-saver, or white point adjustment. You'ld be better off looking for a color perception scale rather than display scale, if you wanted to avoid that. Environmental lighting has big effects on perception though.