"Support for YouTube without a JavaScript runtime is now considered "deprecated." It does still work somewhat; however, format availability will be limited, and severely so in some cases (e.g. for logged-in users). "
The devil is in the details
There are some formats, perhaps the one(s) the user wants, that do not require a JS runtime
Interesting that "signing up" for a website publishing public infomation and "logging in" may not always work in the user's favor. For example, here they claim it limits format availability
"Format availability without a JS runtime is expected to worsen as time goes on, and this will not be considered a "bug" but rather an inevitability for which there is no solution. It's also expected that, eventually, support for YouTube will not be possible at all without a JS runtime."
It is speculated that this format availability might change in the future
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