> As a buyer, how am I supposed to know which manufacturer did their homework and on which laptops?
You first option is to buy a laptop with linux preinstalled from one of the many manufacturers that provides this. This requires no particular knowledge or time. Admittedly, this may lead you to more expensive options, entry grade laptops won't be an option.
Your second best bet is to read tech reviews. Admittedly this requires time and knowledge, but often enough people turn to their tech literate acquaintance for advice when they want to buy hardware.
> Afaik, support for hardware accelerated videoplayback on browsers was broken across the board only three years ago.
Yes indeed, that's something we didn't have. I agree it sucks. Now, all the OSes have their flaws that others don't have, and it's not like the videos didn't play, in practice it was an issue if you wanted to watch 4K videos for hours on battery. Playing regular videos worked, and you can always lower the quality if your situation doesn't allow the higher qualities. Often enough, you could also get the video and play it outside the browser. I know, not ideal, but also way less annoying that the laptop not suspending when you close the lid because of a glitch or something like this.