So lets say:
1. Titanic was sunk intentionally
2. Archeological history is being suppressed (lost civilizations)
3. JFK assassination not what it seemed
4. Moon landing fake
5. 9/11 inside job
6. Water fluoridation is malicious
7. Vaccine development is malicious
8. Free energy technology exists and is being suppressed
9. Children are abducted, sold, and raped by elites
10. Jews control the world
Flat Earth is probably still too new to list.
So, none of them "immediately collapse under scrutiny" in the sense of Flat Earth "go up in a plane and look at the curve".
I would say #8 "Free energy" can be considered "challenged" because anyone who did discover such a thing would begin mining bitcoin, and they would continue to scale their operation until it became so big that it couldn't remain entirely secret.
Likewise I would say #10 can be considered challenged because A. there are lots of jews who don't control much of anything, and B. there are lots of events which go in a way that is not that favorable to Israel.
Lots of people have lots of things to say about all of them, but I'm only calling out 8 and 10 because they're something you can look at and challenge based on first principles deduction alone.
I would say that in essentially all of these cases, if you attempt to debunk it, and begin reviewing the claims in order to know what you're debunking, you *always* run into something that makes it impossible to be sure of what really happened - unless you're willing to "pretend you didn't see that".
I don't have a very high confidence level here, but if I had to put a number on it, I'd say probably 6 out of 10 will turn out to be "true or largely true".
World is a strange place.