Just erased everything and tried to install App Inventor again and now I'm getting this:
Are you running as administrator ?
Yes. 
That is all I know, I do not use Windows...
No problem. Thanks anyway.
Also, do you understand whether you are trying to install the emulator, (to be able to run apps in the emulator), or AppInventor 2 (for your own personal offline use) ?
I'm trying to install the App Inventor Setup software package.
Which is for the emulator
Use Task Manager to end the tasks emulator.exe and adb.exe before reinstalling.
If you are running Windows 11 Home, check the FAQ.