Do people still watch those UFO/bigfoot/JFK/etc. documentaries...

What kind of stupid question is that? No one expects to get definitive proof of anything. When it comes to the aliens, for one thing, you can't get definitive proof. Their technology is too good. Even if you did find some "evidence", all they would do is walk right up and snatch the "evidence" right out of your hand and break the news to you that "you're not supposed to know about that". There's no way you can compete with something like that. We don't have the technology yet to know what is going to happen before it happens and also to appear and disappear from anywhere as needed. I can't even comprehend how something like that would even work, personally (because if you see them do it, if you check the ground afterwards there's no marks or anything, even on grass)!
Documentaries are just for entertainment and for conversational material. You might find out something new, you might not. As for your definition of "Definitive Proof", I don't even think that's possible with bigfoot or the JFK thing, much less with the aliens. I don't think you have really thought that through and considered what constitutes "Definitive Proof".

But its useful intel , gets you thinking, share ideas, maybe learn something new outside of the bible.
Know one has proof of anything, so all you can go by is first hand witness accounts.

And witness credibility ie

So if a fella named Bubba dressed in his one piece 1920 coveralls stands in front of me with his thumbs tucked in the side of his suspenders tells me, that last night while huntin for gators in a local Louisiana swamp, afta swigging on a half gallon jar of 100 proof moon shine says he saw a alien messin with his Gators, i might be concerned about is state of mind, his credibility as a witness to relate accurate factual information.

On the other hand if an astronaut, airline pilot , fighter pilot who are familiar with most types of aircraft and their technical abilities says he spotted an object travelling and maneuvering in ways human bodies could not withstand, i would tend to believe their story over old Gator catching Bubba above.

Get it OP.

documentaries used to be a good source of info, such as “a funny thing happened on the way to the moon” and “everything is a rich mans trick”. But the history channel and discovery basically obliterated the usefulness of the documentary. They are 99% popcorn bullshit now, with rare exceptions like “citizen four”. What I’m trying to say is that they documentary medium has all but worn itself out.

Podcasts and radio are mostly shitt at this point too. They have been commercialized into oblivion with the exception of fringe podcasts like the Tom woods show. The best source of info anymore is long discursive lectures you can find on YouTube and wading through the tons of info and shit on alt social media.