Comment 2 for bug 1837209

Tested Oliver's suggestion and indeed it does work if the overlay is removed but I assume that the overlay is there for a reason. Furthermore, extracting the psplash binary from the psplash initrd and running it after boot has concluded (at which point /dev/fb0 exists) works successfully which suggests there's no issue with the framebuffer itself, just that the framebuffer doesn't exist (presumably due to the aforementioned lack of kernel modules in the initrd) at the (very early) point in the boot where psplash is executed.