Assuming your EDID is named dummy_2560_1600_120.edid
This is confirmed working on the latest CachyOS and Nvidia RTX 5090, Gnome, Wayland. Need to re add to the bootloader and regenerate initramfs after each update.
```
sudo cp ~/dummy_2560_1600_120.bin /etc/X11/edid/dummy_2560_1600_120.edid
```
```
sudo chmod 644 /etc/X11/edid/dummy_2560_1600_120.edid
```
```
sudo mkdir -p /usr/lib/firmware/edid
```
```
sudo cp /etc/X11/edid/dummy_2560_1600_120.edid /usr/lib/firmware/edid/
```
Check:
```
sudo ls /usr/lib/firmware/edid/
```
Add the EDID to bootloader (need to re-add after every update, can add before restart):
```
sudo nano /boot/loader/entries/linux-cachyos.conf
```
At the end of options add:
```
drm.edid_firmware=HDMI-A-1:edid/dummy_2560_1600_120.edid
```
Save and exit.
Add the EDID file to mkinitcpio config:
```
sudo nano /etc/mkinitcpio.conf
```
Find the FILES=() and replace with:
```
FILES=(/usr/lib/firmware/edid/dummy_2560_1600_120.edid)
```
Save and exit.
Regenerate initramfs:
```
sudo mkinitcpio -P
```
And reboot.