Indeed, clone display with the 2xhdmi of the pi4 was what I was originally looking for and what is currently in use with the help of an hdmi splitter.
Might as well just stick with that (getting libreelec to use clone mode seems to exceed my knowledge by far and i don´t want to switch to some other os) or do what a reasonable hipster should do and just get another pi 
Guess you´re right, all I did was hitting sth by accident.
As far as I understood from further googling around I´d basically be best off using a less compact OS and install kodi there... I will do the reasonable and get another raspi with libreelec, who knows, that might offer synergies.
Thanks for your Time and patience, Guys
Good one, thank you. Tried that from the raspi forum
# Test Screen Mirroring
max_framebuffers=2
xrandr --output <HDMI-2> --same-as <HDMI-1>
and it kind of changed something. the rainbow is gone, now the second screen is black
Don´t have much of a clue what i´m doing here but will investigate further when having time.
Fair point, though i really have scenario one screen at the desk for having some background noise while working, gaming etc, one at the bed for watching series and such on a more comfortable base. for me it would be mirroring, not stretching/expanding.
I was just thinking something might have come up since the last post since the 4 is longer around now.
Thanks for the feedback, though. Running on an hdmi splitter atm, might as well get another raspi and quit whining
Hello all and thanks to the Devs from a Newb
Ran into the same issue on a fresh install yesterday, haven´t found a clone-option somewhere in Kodi... is there maybe a fix for that in librelec configs?
"Disable other screen" isn´t ticked, works generally since it IS showing the rainbow, but no kodi on display 2 
