EULA and TOS are not legally binding in the way people think they are.
If it just prevents you from using it on the game, that is fine and likely legal.
If it is damaging the hardware or software in some way permanently, it is most definitely illegal.
Also it's been found that Vanguard is not turning off and remaining in effect while people try to do other things, preventing them from running other apps and games.
The idea of "it just effects the cheaters" is stupid and not an argument.
Let’s walk through how that courtroom drama plays out:
Cheater: "Your Honor, Riot bricked my $6,000 PC!"
Riot: "Actually, we just updated Vanguard to enforce standard Windows IOMMU security protocols. If they unplug the illegal hardware cheat device from their motherboard, the PC boots perfectly fine."
Judge: "Wait, so your computer works, but your specialized cheating hardware doesn't?"
Cheater: "Yes! It’s property damage!"
Judge: [Bangs gavel so hard it breaks] "Case dismissed. Pay Riot's legal fees."
You cannot sue a company because their security system successfully detected your exploit. Riot didn't destroy anything; they just rendered a cheating device useless for cheating. If you spent thousands of dollars on a DMA card just to click on heads in Valorant, your only legal recourse is to sue your parents for giving birth to someone so stupid.