write to config.txt not sys, sorry
It’s good to know you have a solution, however you got it.
I later realised that my Mint solution cannot (easily/not at all) be applied in the RPi context as not all the tools are available.
I suggest that the original problem may lie in the EDID information supplied by the monitor/TV being incorrect/unavailable.
the command tvservice can be pressed to give quite a lot of information - including a dump of the edid info.
Derek
I have this problem too (Pi 3), display resolution fixed at 1824 x 984 but my monitor is 1920 x 1080 (HP Pavillion 22xi), hitting Detect Monitors does nothing… I have tried to add a new mode using xrandr but get an error ‘Failed to get size of gamma for output default
warning; output to HDMI1 not found; ignoring’
UPDATE: SOLUTION FOUND
in /boot/config.txt uncomment disable_overscan=1
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