Hello! I've just installed Slackware current to my i9 12900 and it works from the box, thank you!
I installed it twice:
1. Without eelilo, to the same disk with Devuan (Devuan controls EFI partition)
2. With eelilo, to another separate ssd disk (also Slackware asked me to add boot option to uefi, and I said yes)

Questions:
1. The main question is: I cannot see new boot option in UEFI, and also I don't know how to add boot option to UEFI on Gigabyte Aorus Elite AX. Please, how to add boot option there? All other OS added boot options to my uefi, but slackware had not.

2. When I run under Devuan `update-grub2` it does not find and does not add Slackware that is installed to another partition on the same disk. Can I add it with my hands? Could you provide example grub menu entry for that?

3. When I run under Devuan `update-grub2` it finds successfully Elilo partition on another ssd disk and add corresponding grub menu entry, but this entry does not work, because it has wrong file path here:
chainloader /EFI/elilo.efi/elilo.efi
I edit it like this and boot fine to Slackware:
chainloader /EFI/Slackware/elilo.efi
It's not convenient that update-grub adds wrong menu entry. I tried to mount elilo partition to some path for Devuan scans it in proper way, but all the same. Is there any advice for my interest?

> 1. The main question is: I cannot see new boot option in UEFI, and also I don't know how to add boot option to UEFI on Gigabyte Aorus Elite AX. Please, how to add boot option there? All other OS added boot options to my uefi, but slackware had not.

I think I have not added necessary flags or may be FS type. This is my Devuan efi boot partition type that presents in uefi:
# blkid /dev/nvme0n1p1
/dev/nvme0n1p1: SEC_TYPE="msdos" UUID="C820-B4F1" BLOCK_SIZE="512" TYPE="vfat" PARTLABEL="EFI System Partition" PARTUUID="83093a7d-c014-4fc7-a5a2-6ea7fc341c4b"

And this is my Slackware efi partition type that does not present in uefi:
# blkid /dev/sda1
/dev/sda1: UUID="29A7-01ED" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="ba4b46d6-cf00-4980-8b2b-4c4ca890e470"

Should I add some flags to /dev/sda1? which and how? and how then add uefi boot option?

take a look here https://www.atulhost.com/how-to-disa...comment-page-1

Boot into Devuan, create a /boot/grub/custom.cfg and copy the menuentry for slackware from /boot/grub/grub.cfg and edit for the correct changes.

The other option is to manually create a menuentry in the custom.cfg to boot slackware kernel directly.

If you run "/usr/sbin/efibootmgr" ("man" or --help would help) you will see what entries and in what boot order have been added into firmware. There you can change order, remove old or add new entries that would then appear right in your BIOS/UEFI "Boot Order" menues either under the "Boot" tab or the Order menu usually accessed with an "F Key". Once you have verified firmware has it, so should any bootloader that handles EFI boot and seeks bootable kernels.

You might like rEFInd for a bootloader that's not tied to any one OpSys, is configurable basically like elilo but is easier to accommodate multibooting.