Among other things, UNIBIOS allows:
The latest UNIBIOS is provided in the updated FinalBurn Neo romset.
Hotkey + B and go to Options.
Neo-Geo mode setting.
Use UNIBIOS bios.

Y + B + A buttons (on the original controller, the buttons correspond to C + A + B respectively).

To exit, use the X button (the C button on the original controller).
To access the in-game menu, you must press and hold the X + A + B + START buttons.
To access the dip switch menu during the UNIBIOS boot screen, press and hold Y + X + A (on the original controller, the buttons correspond to C + D + B respectively).
To display the blood in Metal Slug, once in the dip switch menu:
SETTING UP THE SOFT DIP.
SLOT1 METAL SLUG.
BLOOD and change from OFF to ON.
To navigate through the menus, press A to confirm and press C to go back. Change the desired values with A and B.
Neo-Geo requires a BIOS file named neogeo.zip.
/recalbox/share/roms/neogeo
or
/recalbox/share/bios
000-lo.lo
japan-j3.bin
neo-epo.bin
neo-po.bin
neodebug.bin
neopen.sp1
sfix.sfix
sm1.sm1
sp-1v1_3db8c.bin
sp-45.sp1
sp-e.sp1
sp-j2.sp1
sp-j3.sp1
sp-s.sp1
sp-s2.sp1
sp-s3.sp1
sp-u2.sp1
sp1-j3.bin
sp1-u2
sp1-u3.bin
sp1-u4.bin
sp1.jipan.1024
uni-bios_1_0.rom
uni-bios_1_1.rom
uni-bios_1_2.rom
uni-bios_1_2o.rom
uni-bios_1_3.rom
uni-bios_2_0.rom
uni-bios_2_1.rom
uni-bios_2_2.rom
uni-bios_2_3.rom
uni-bios_2_3o.rom
uni-bios_3_0.rom
uni-bios_3_1.rom
uni-bios_3_2.rom
uni-bios_3_3.rom
uni-bios_4_0.rom
vs-bios.rom