About five years ago I posted about getting UEFI to work with Slackware and elilo. I made it a bit more confusing than it needed to be. To make an initrd, you just need to go into the /boot directory as root and use the command geninitrd. Slackware will automagically make the proper initrd.gz so your system will boot.
Then copy the generic and huge kernels as well as initrd.gz to /boot/efi/EFI/Slackware. eliloconfig will create an elilo.conf file there but it will only create one entry. You can make your own. The syntax is very similar to lilo. Here's my current elilo.conf. I noticed there was some weirdness in the one from five years ago. This is for the latest kernel as of this writing on my fancy new WD Black NVMe drive. Zoom!
chooser=simple
delay=100
timeout=100
prompt
#
image=vmlinuz-generic-5.15.94
label=generic
description="Slackware 15.0"
initrd=initrd.gz
read-only
append="root=/dev/nvme0n1p2 vga=normal ro"
image=vmlinuz-huge-5.15.94
label=huge
description="Slackware 15.0 Huge"
read-only
append="root=/dev/nvme0n1p2 vga=normal ro"
