Ok, what are people playing, when they play 'fast'

I was gonna post this on Thursdays no stupid questions, but I was busy yesterday and it slipped my mind, and I already missed posting it the week before that so I just posted it today because I can't go another week without figuring this stuff out. Have mercy on me :)??

I've been watching Chappers, Ola Englund, etc. on YouTube forever, and I never understand what any shredder is playing. I've been playing for about 8 years, and was originally taught through tabs, so I have absolutely no concept of theory. Since then I've become (I think) a pretty solid Rhythm player, I've developed most of the major guitar skills very well, besides the whole shredding thing. I've been trying to get started on learning but all I find are videos like, this is how you hold your pick, or this is how you train your fingers, but I have no idea what they are actually playing for me to practice.

I've heard things like penatonic scale being slung out, but If I learn this will I just be sitting there playing this scale, do I have to link it to other scales, I just haven't got the slightest a clue. The only thing I really know is that people are playing in the Key of something. But other than that, i'm lost.

So r/guitar, i'm selflessly asking for you guys to give up your time to hopefully steer me in the right direction, so I can expand my ability.

What should I do/play/watch that will teach me the actual notes and theory behind what these guys are playing, and is not just a youtube channel or paid guitar lesson thats gonna tell me to alternate pick with my wrist when I've been out tempo'ing fight fire with fire