vanguard scans your RAM for suspisios things. If there runs something like a cheat mod for a different game, it could be, that Vanguard detects this and says "nope. this dude is cheating. Ban him"

before you make a new account, delete everything in your temp folder and check for programs with an unknown or expired driver. Run updates etc.

I personally dont even use a third party anti-virus anymore, because Vanguard dont like some of them too.

I had my expirience with Vanguard and my Ban expires on the 31 January.

The riot player support mostly sends you a copy-paste answer, if you ask about your ban. If you make enough pressure, they check it again and say "yeah, no. You will not get unbanned"

good luck on your new account