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I booted up into Monterey, to try this myself.
Safari offers me the 4k option for the "Japan" video.

Not sure why the OP isn't seeing the option for 4k.
Hmmm.... what Mac do you have, and what resolution is the display set to?

On my "regular OS" (Mojave) Safari DOES NOT offer me a 4k option.
Simple solution:
Use another browser. Most other ones WILL offer 4k with YouTube.
 
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Could it be related power settings? There is a setting "Optimize video streaming while on battery power" on battery settings if it is on you can try turning it off.
 
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