Lakka RPI4B themes wallpaper

The documentation on Lakka needs to be updated and more info added because some things have changed over time. For the Raspberry Pi 4B I want to create wallpapers for my system but I dont know what is the max resolution supported and if it shows it properly.

The old outdated documentation says 1440 by 900 but I had plain simple wallpaper of Full HD (1920x1080) show just fine. Is there higher resolutions supported? I also wanted to make my own theme with slightly bigger icons for systems but lack of documentation prevents me from wanting to waste time with it if it doesn’t actually work.