For udemy classes though it is hard to know what is timeless knowledge vs what is outdated crap starting out.

That is why there isn't much else to go but the heuristic of the most new class with the most ratings.

True, but sometimes you need a cheap course about some seasonal garbage.

A few years ago i happily spent 12€ on a course about gitlab ci that saved me quite a bit of time reading documentation and got me started within an afternoon. I had no previous experience with gitlab, but i was well versed with git.

Those were money well spent, for example.