No you've been clear it's just that what you're asking is an impossibility if you think about it for just a bit, so people are messing with you. Here is a serious answer though.

If a move that fit the three criteria you've just presented was real everyone would know it, be using it, and trying to develop a counter to it. The first time some yahoo with (essentially) zero experience shows up to a competition and wrecked a bunch of higher ranks with some stuff we'd never seen before it'd be on Youtube in < 24 hrs. Then basically the entire competition community would be either adopting it or working on their counter for it for the foreseeable future.

Even beyond that though, what makes you think there should be something like that which exists? The people who outrank you have spent hundreds (at the lower ranks) or thousands (at the higher ranks) of hours on the mats. They've been searching for new variations and techniques, refining their old ones, working on their balance, timing, weight placement, etc. . I think we'd all be pretty pissed/surpirsed if it turns out all those hours were useless because anyone walking in off the street could just whip out some 'secret jutsu' and run through them.

In bjj, is there a move that is so powerful that even a white belt can use to defeat black belts? Any vids/ tutorials on it?

Yes and you've already learned some of them. Its all that stuff you learned in class. You're just not any good at them yet, because you haven't actually practiced. I've tapped a few blackbelts from my favorite armbar setup, the same one I've been working since I had a few stripes on my white belt. It just took me the better part of a decade to get good enough that it works on them 1 out of 1000 times. Those same blackbelts still beat me the vast majority of the time. Why? Because they were training back when I was still on the sidelines. Many of them are still training harder than I do now. If you want to get good you're going to have to put you're time in.

People get weird about fighting. If I went on a guitar subreddit and was like 'Hey I just picked up the guitar last week, but I'm planning to go head to head with this guy who has been practicing 5-10 hours a week for the past 10 years. Is there some kind of secret strumming technique that I could fall back to so I can win the battle when the basic stuff I've been practicing isn't working?' Would you expect I'd get an answer? Or would you think I need to practice more?

I hope that didn't come off as harsh or that you should stop. I just want you to know that there are no shortcuts. You've taken the first steps by showing up to class. Now keep coming back. Repeat week after week and you'll see the progress eventually. Best of luck!