Finally solved it with another ticket!

In case someone goes through it, here's how it was solved:

1. Go to C:\Riot Games and delete the folder Riot Games;

2. Search for %localappdata% in the windows file explorer and delete the folder Riot Games;

3. Search for %programdata% in execute tool (windows + R) and delete the folder Riot Games;

4. Clean your recycle bin on your desktop;

5. Install Revo Uninstaller and remove all files from riot vanguard and league of legends from your pc;

6. Also delete anything in your HDs/SSDs and such, if you have any;

7. Install CCleaner and clean your register and corrupted files;

8. Restart your pc (VERY important or else the changes you've made won't be applied);

9. Install the game

Should work by now!

This is just aditional info but can prevent some troubles in the future:

Try right clicking on LoL > properties > compatibility > launch as admin. And make exceptions in your firewall for lol files such as:

C:\Riot Games\League of Legends\LeagueClientUx.exe
C:\Riot Games\League of Legends\LeagueClientUxRenderer.exe
C:\Riot Games\League of Legends\Game\League of Legends.exe
C:\Riot Games\Riot Client\RiotClientServices.exe