I did the ugliest thing I could do because I was already tired of trying everythin with no results. I am in windows so I hide the taskbar and made a "false" fullscreen configuration, I have 1920 X 1080 resolution so I changed the values for -1 pixel for each property in the retroarch.cfg XD
video_fullscreen_x = "1919"
video_fullscreen_y = "1079"
so now I have a fullscreen that is not fullscreen but has no lag