Is that just AMD? On my thinkpad X270 playing videos in Firefox is just a mess. All sorts of problems while Chromium is just fine. It's also fine on a copy of my system that I run on a thinkcentre tiny.
I do believe Chromium still has to be patched to support HW decode via vaapi, while recent Firefoxen turn it on out of the box. So it's likely that Chromium is using software rendering, bypassing any driver-related bugs.
Chromium doesn't document this but they support hardware video decode on Linux. Works best on Intel iGPU. AMD needed some patches to get it working using Vulkan IIRC and Nvidia is Nvidia.
What did you have to do to get it to work for Intel iGPU? Passing all combinations of command line flags never made it work.
intel_gpu_top showed both Video and VideoEnhance markers signaling hardware decode as inactive, and all commenters on message boards that I came across essentially came to the same conclusion, that it doesn't work at least at the time I as trying a few months ago. I think it was that Chromium devs don't support it and block it from functioning in the code because of this or that upstream dependency not being stable.
Have no problem using just this flag --enable-features=VaapiVideoDecodeLinuxGL on a laptop with HD Graphics 500. And I even think that flag is passed by default now.
Key thing is to make sure you are playing back supported codecs when checking for hw decode. E.g YouTube randomly forces av1 on clients and some older hardware don't support hw decode for it.
Also some distros like Fedora and OpenSUSE ship with partial codec support in their installation media.
An easy way to make sure you have all the right drivers in place is to test this in one of the Chromium flatpaks.
Though I have to state hardware video playback is not yet officially supported and it has broken a lot over the past due to this fact and the quality of the different GPU drivers in question here. The Chromium devs don't explicitly block vaapi on Intel hardware.
I always had all the codecs and Vaapi on Firefox worked fine, but could specifically never get Youtube on Chromium to use GPU decoding, that was the main problem you're reminding me.
In this past year, I've since moved to Windows after like 7 years of constantly messing and tweaking Linux to kinda sorta almost for some stretch of time get all the things to work after spending hours looking for the right configuration. Look at how long this thread is, for example[0]. Or here most saying it still doesn't work[1] and the flags constantly change. Before Linux I was about 6 yrs on Mac. I hadn't used Windows for so long, it actually felt weird to have so much hardware and software support for anything I ever need to use.
I'll take your word for it that Chromium sometimes uses hardware decoding now. But as you say, and they should put that slogan on a T-shirt: "Linux on Desktop: not officially supported and it has broken a lot over the past due to lack of support and quality of driver". I wouldn't really characterize that as "have no problem using". It feels nice to have a system that just works without all that hassle and tweaking so I can just get actual work done, or watch Youtube efficiently without brittle configuration, no window manager bugs etc.