I’ve got a Raspberry Pi 4 running Raspberry Pi OS, an HDMI monitor, and a female-male HDMI panel mount cable connected to an HDMI-micro HDMI adapter. When I hook my monitor up to the extension cable, I get no video output (although the monitor briefly turns on).
The extension cable works fine connected to my laptop.
The Raspberry Pi works fine connected directly to the monitor using the HDMI-micro HDMI adapter.
config.txt has had these lined edited:
hdmi_force_hotplug=1 hdmi_group=1 hdmi_mode=1 config_hdmi_boost=4
I’ve also tried just setting
EDIT: Following some of the advice in this forum thread, I've also tried the following
config.txt options (to no avail):
hdmi_ignore_edid=0xa5000080 hdmi_group=2 hdmi_mode=81
And to confirm, I'm using the HDMI0 port.