I've read a while, and I couldn't find anyone that has rooted this specific version. 
I'd already tried that method and nothing. However, Now I could root it!!!! It seems, at least in my case, that the problem was Windows 10. I've failed with all methods in Windows 10. The first I tried in Windows 7 was this one, and VOILÀ!I rooted 21Q using this method http://forum.xda-developers.com/lg-g3/general/guide-root-method-lg-devices-t3129197