After update CoreELEC 8.90.1 to 8.90.3, when i choose 1920*1080 resolution, i have low fps, someone with the same problem?
It would be helpful if you could provide what you are playing ie the codecs being used, and of course a debug log.
But best to first install the new version 8.90.4 and see if that fixes the problem.
Have you enabled resolutions and frame rates in Whitelist? I’m guessing not.