GRUB and boot questions

[mundodisco]

I have just installed Recalbox 6.1.1 (stock version, downloaded from this site: I say this because a user thought I was using an illegal image downloaded from another site, but he misunderstood) on my desktop PC. It is a Dell desktop with an old core i5 (gen 3) with an ATI Radeon HD 4350.

The problem is: on PC, loading time is longer than with Raspberry Pi 3, and "uglier": GRUB menu appears (I know how to reduce the time it waits before booting, but I am not sure how to make it not appear at all). And, it does not load an image during boot (just black screen). While the Raspberry Pi version almost instantly shows an image, and boots faster.
Does anyone know how to edit GRUB in Recalbox and/or another config file to make GRUB disappear and show images during boot?

Regards,
Gabriel

[Zing]

@mundodisco Read this tutorial, search for GRUB in the tutorial and you will have a good part of the information you want, from there the rest I think you will understand, even if it is not exactly what you are asking for:
https://forum.recalbox.com/topic/17464/dualboot-recalbox-windows-sur-pcs-laptops-avec-bios-ou-uefi-27-04-19?_=1585857631180

[mundodisco]

@Zing Thanks for your previous answer. With the post you suggested, I managed to delete an entry of the GRUB menu (the verbose one), and to reduce the time of waiting prior to enter in the default option.
However, there are still two things I wonder how to do it:

1. how to prevent GRUB from appearing at all (if possible);
2. how to load a static image while booting (before EmulationStation starts), to avoid the black screen.
   Thank you very much in advance,
   GABRIEL

[Zing]

@mundodisco I don't have the knowledge to answer this question properly, but Recalbox is a LINUX-based system, so research on how to edit GRUB on Linux and try to do the same on Recalbox, the basic commands should work.
To change the GRUB image, I know that there is GRUB CUSTOMIZER, but I don't know if it is possible to install it on Recalbox, I never tried it, it may not be possible, because Recalbox abdicates many features to reduce the space used by the system.
See this link, it might help you:
https://unix.stackexchange.com/questions/422104/make-grub-boot-on-default-without-waiting

Note: When finished, please post the solution here, maybe your answer will help other people with the same problem.