How to duplicate two monitors on raspberryPI 4B using only RetroPie 4.8 (RPI 4/400)

[MiroKostovBG]

Hello,

I'm using the RaspberryPI 4B model with the 2 micro HDMI outputs and I'm trying to duplicate/clone/mirror the main monitor to the second monitor. By default they are extended and the second monitor shows different content. (It does not show retroPie/EmulationStation/Games, but shows raspberryPi logs etc., when i go to raspi-config for example it is shown in both monitors)

I am new to this and I tried the whole day searching for solutions on the internet but none of them helped me in my situation.

My question is simple, can I by default make the raspberryPI 4B where currently I have only RetroPie 4.8 (RPI 4/400) installed to mirror the monitor by default on Raspberry level, so that I do not need to configure every single thing that starts but rely on some "factory" setting that will mimic as if I have purchased an HDMI splitter instead using the two micro HDMI ports, which also relates to sound as I would like to get the sound on the second monitor as well.

I have two identical monitors, with identical resolutions I just need the raspberry not to extend them but to clone one to the other. I have read that many try to have different images on the different monitors or struggle with orientation/resolutions/visible content, or try to extend content in custom way. None of this applies to me. At this point I have exhausted my ability to know what to search for so any suggestions in that direction would be great.

Most of the guides I'm finding require me to use xrandr but It does not work as from what I read there is no X11 in the installation.
I'm searching for "factory" setting that decides that it will extend the monitors so that retroPie and everything is showed to the two monitors at the same time.

Any help would be greatly appreciated, the other way to solve this would be to buy an hdmi splitter but I would like to take advantage of the two hdmi micro ports the raspberryPI 4B has.

Pi Model or other hardware: (RaspberryPi 4B 2GB)
Power Supply used: (official Raspberry Pi power supply)
RetroPie Version Used (4.8 RPI 4/400):
Built From: (Raspberry PI imager v1.7.5)
USB Devices connected: Two 8bitDo SN30 controllers connected with USB.
MicroHD devices: Two DELL S2340L monitors with the official raspberry microHD to HDMI cables.

How to replicate the problem:

1. Install RetroPie 4.8 RPI 4/400 from the official Raspberry PI imager v.17.5)
2. Start RetroPie

OBSERVED:
RetroPie starts on main monitor.

DESIRED:
RetroPie to get cloned on both monitors on system level so that the image is just cloned and not extended.

[mitu]

Not possible in software without X11, which - as you found out - is not used and installed by RetroPie. An HDMI splitter is the easiest alternative.

[MiroKostovBG]

@mitu Thank you very much, I have purchased a splitter and solved the issue for 20 bucks.