I'm also starting to play with the latest Generic build on a laptop that is connect to an external screen via a DisplayPort to HDMI cable.
On boot up I get the RetroELEC boot splash screen on both Laptop and external screens.
It boots up into Kodi, but only the Laptop screen is enabled, and I can't see anywhere in the Kodi System Video settings to change displays.
If I switch to Desktop I get the display on both screens.
If I switch to RetroArch the laptop screen is active, but I can activate the external screen by switching to display #2, but it reverts to the laptop screen when I launch a MAME game.
On the generic LibreELEC build I used to use xrandr commands to active the external screen and disable to laptop screen, but xrandr doesn't appear to be in the RetroELEC build.
Is sway meant to replace xrandr ???
I found the sway config and did some reading, but when I was booted into Kodi I couldn't get info on sway
RetroELEC (community): devel-20200716014709 (Generic.x86_64)
LibreELECusb:~ # swaymsg -t get_outputs
00:00:00.000 [common/ipc-client.c:67] Unable to connect to /run/sway.sock
Is there a set of commands (possibly to put in an autostart.sh) that can control/force external displays in the various environments for Kodi, RetroArch, MAME, Desktop ?
Thanks.