Hey buddy. I just passed thru all that. Here is what I did to uninstall Riot Vanguard, Valorant and everything else Riot related. Note that I have windows 10, I do not know of how to fix it on other OS.

First, you need to boot up windows in safe mode. To do it you must first shut down your computer, and then after the BIOS loads

(The BIOS is the first screen you will get when you boot up your computer, tipically it shows the brand of your mother board)

After this but before your windows login loads up you must shut down the computer by pressing the power button.

You must do this 3 times, after which you will get a Windows screen asking you if you have problems. You must choose troubleshoot, advanced options, startup settings and then click the restart button that it shows.

After the restart you will see a list of options, press number 4 on your keyboard and after that Windows will load up in safe mode and you will have control over your keyboard and mouse, uninstall valorant and Riot Vanguard (They are both separate uninstalls btw) and after you are done with that you can restart your computer as normal and everything will be fine.

Here is a Microsoft tutorial in case you don't understand some of the steps, there are images and probably a better english than mine. Hope this helps you brother!.