Is this a quasi-captcha because of some legal reasons? I would assume math problems are easy to solve for a computer (easier than for most of the humans, actually).
It's just a flippant way of saying "hiding the URL or parameters behind running JavaScript that serves no other purpose than obfuscation". See also this commit:
Of course this is easy to solve, but every layer of obfuscation they add generally requires someone to go and work around it in yt-dlp. It's mutually assured time waste on both sides.
