Firmwares often provide initial graphics framebuffers so the BIOS,
bootloader or kernel can show basic video-output during boot for
user-guidance and debugging. Historically, x86 used the VESA BIOS
Extensions and EFI-framebuffers for this, which are mostly limited
to x86 BIOS or EFI systems.
This option, if enabled, marks VGA/VBE/EFI framebuffers as generic
framebuffers so the new generic system-framebuffer drivers can be
used instead. If the framebuffer is not compatible with the generic
modes, it is advertised as fallback platform framebuffer so legacy
drivers like efifb, vesafb and uvesafb can pick it up.
If this option is not selected, all system framebuffers are always
marked as fallback platform framebuffers as usual.

Note: Legacy fbdev drivers, including vesafb, efifb, uvesafb, will
not be able to pick up generic system framebuffers if this option
is selected. You are highly encouraged to enable simplefb as
replacement if you select this option. simplefb can correctly deal
with generic system framebuffers. But you should still keep vesafb
and others enabled as fallback if a system framebuffer is
incompatible with simplefb.

If unsure, say Y.

source code:

drivers/firmware/sysfb_simplefb.c