Thanks, WayneWWW.
I have changed the hdmi cable as you say to a better non-chinese hdmi good-quality cable and the problem is solved. When I connect the Jetson Nano to the 1920x1200 monitor, you can see much more options to choose a different resolution.
Anyway, I think that this is not the problem that doesn’t let me change the resolution to 854x480 with xrandr command (I have to test it with the new cable when I finish to solve my desktop PC problems). I think that there are problems related to nvidia systems as it is described here: [url]xrandr - ArchWiki
I post a picture of the second problem:
[url]jetsonBlack.jpg - Google Drive
I have to say again that I think that this problem is due to the change of the /usr/lib/aarch64-linux-gnu/libGLX.so.0 file with the /usr/lib/aarch64-linux-gnu/tegra/libGLX_nvidia.so.0 file and the renaming of this last one with the libGLX.so.0 name, because this is a problem that appears only some time later after doing this (if I format and reinstall Jetson system image in the microSD this problem dissapear).
Thanks again.