Vanguard takes screenshots of your PC every time you play a game. Every time you play a game a function is called to screenshot your PC’s screen, in case Vanguard thinks you might have something suspicious, it screenshots your ENTIRE PC screen (all monitors).
Edit: Not trying to spread false info this was shared to me via a friend and there is other data to back up that this is real https://www.unknowncheats.me/forum/anti-cheat-bypass/634974-vanguard-taking-screenshot-pc.html
https://www.unknowncheats.me/forum/valorant/484475-vanguard-screenshots.html


it simply wouldn’t trust the client with anything the player shouldn’t know, to minimize cheating potential. valorant does this, and made a blog post about it. also, player movement could be analyzed server side to attempt to distiguish between cheating and legit.
I think client side invasive anti cheat is likely more effective than this, but its a cat and mouse game. if the anticheat was server side and good, there isn’t anything to attack