Huh. Now that's weird.
I tried what you described (thank you very much for that!), and while the script works like a charm, for some reason fbi fails to load the 1920x1200 splashscreen. It literally returns a black screen with
/home/pi/RetroPie/splashscreens/retropie-extra/rookervik-pixel-16x10.png: loading FAILED
written at the bottom. The weirdest thing is that if I run
sudo fbi -T 2 -once -t 20 -noverbose -a -l /etc/splashscreen.list >/dev/null 2>&1
after start up, mimicking the syntax in /opt/retropie/supplementary/splashscreen/asplashscreen.sh, the image is shown normally!
So close, yet so far! Any ideas?
EDIT: UN-FREAKING-BELIEVABLE! That was happening because I’m using USB auto-mount for loading roms into the system. For some reason, that option also overwrites the splash screens directory, but the pendrive is only mounted AFTER the splash screen is actually shown on startup. Hence, when I moved the stretched image into the directory, I was actually moving into the pendrive, which is ignored by the Pi on startup! All I had to do was unmount the pendrive, copy the file into the SD card and it worked! 😁 Thank you very much once again for all the help!