[RPi5] GUI colors and resolution problem

I have noticed some strange behavior with my new LibreELEC setup when playing 4K content:

1. During boot, the LibreELEC splash screen appears in the top-left corner and occupies only about one quarter of the display.
2. The GUI colors change whenever I open my projector’s on-screen menu. While the projector menu is active, all text and icons become noticeably whiter and actually look better.
3. I need to set the maximum resolution manually in the display settings. If I set the GUI to 1080p, enable the 4K modes in the whitelist, and configure the player to adjust the display refresh rate to match video playback (on start/stop), the intention is to keep the GUI at 1080p and switch to 4K for movies. However, when doing this, the image again shows up in only about one quarter of the screen.

I have already tried resetting /storage/.kodi/userdata/guisettings.xml and forcing a new one, but it didn’t help. This is a fresh Raspberry Pi 5 installation, but I restored a backup from my previous Pi 4 to keep all apps and configuration.

Do you have any idea what might be causing this? I would appreciate any clues on where to investigate.

I think it has been always 1080p and that is the reason. It is connected to 4k projector so it is then just 1/4 of scree. When I applied your suggestion the booting logo was the same and then the gui sticked to it (1/4). I had to move panes to make it fullscreen again. Doing it all I selected 1080p as a GUI resolution but while playing the 4k movie it is only 1/4 of the screen. So not changes in general.

I am using the adapter, I need 10 m HDMI cable. I have replaced the adapter with the cable, it goes to spliter then the spliter sends 4k to projekctor and 1080p to TV, seems to be fine. I left gui in 4k.

There is one more think, I can hear a little noise in my 2.0 speaker sending signal from spdif digi standard, I could not hear anything on RPI4.

I have tested various cables, splitters and other components. Everything seems generally fine, however, I still occasionally experience an issue where, after booting LE, the logo appears in only one quarter of the screen. I have also noticed that some 1080p movies display in the same way (only 1/4 of the screen).

At the moment, I am using two micro-HDMI to HDMI cables. HDMI1 is connected to the Sony AVM and is used only for audio output. HDMI0 goes into the EZXCOO splitter, where one output (with a scaler enabled) is connected to an older 1080p TV. The other HDMI output from the splitter goes directly to the projector.

My config contains only:

# HDMI0
hdmi_force_hotplug:0=1
hdmi_enable_4kp60=1

#HDMI1
hdmi_force_hotplug:1=1
hdmi_blank:1=1                   
hdmi_drive:1=2                   
hdmi_ignore_edid_audio:1=0       


audio_pwm_mode=2
disable_overscan=1
dtoverlay=hifiberry-digi

# EDID
drm.edid_firmware=HDMI-A-1:edid/jvc.bin,HDMI-A-2:edid/sony-pure.bin
initramfs edid.cpio 0x3c00000

[all]
include distroconfig.txt

and cmdline.txt

boot=UUID=0111-4635 disk=UUID=67e94c52-7c1c-4e07-b241-4d3919401f7a quiet console=ttyAMA10,115200 console=tty0 video=HDMI-A-1:1920x1080M@60D