Google chooses codecs based on what it guesses your hardware will decode. (iPhones get HEVC, Android gets VP9, etc) They just didn’t put much thought into arm based home devices outside of a specific few like the shield.
My by now rather ancient rk3399 board can hardware-decode both at 4k 60Hz. Which has nothing to do with the fact that it's aarch64, but that Rockchip included a beast of a VPU (it was originally designed for set-top boxes).
How about, dunno, asking the browser what kind of media it would prefer?
This issue was detected when running Firefox on Linux on Apple silicon. Firefox on Mac just identifies as x64.
It's probably not on purpose by YouTube. It's stupid they put restrictions on some heuristics to begin with but maybe because otherwise people would think YouTube is not loading properly while it's the software decoding on the not capable arm PC that can't handle the resolution.
Seems like my Samsung TV app is being hit by stuff too, I had 5 unskippable ads and can't seem to get stable 1080p at 60fps any more despite gigabit fibre and cat6. Meanwhile getting 4k on my YouTube app on Android on WiFi.
Go figure.
YouTube is so desperate to fight this war that they're harming legitimate watchers meanwhile my rockpi running Android TV seems to keep running sTube just fine.
That's what I figured, but every article I've seen on this calls out Linux specifically. I'll have to give it a try from my Surface Pro X when I get home and test.