The weird long /dev/disk/… I used comes straight from your Pastebin. It’s a unique link to the your EFI partition, but sadly efibootmgr can’t use that to register your bootloader. The Arch wiki example command leaves X and Y for you to fill in, and you need to find the X and Y for your system to make it work. They’re different for every computer so I can’t tell you what they are.

On my system, the EFI partition is /dev/disk/by-partuuid/2fbab938-cc71-407a-996a-874d4486fca8. I used the ls command to find the right information in my example above, but realpath is probably better, so I’ll use that in this comment.

I can find out the right X and Y for my system using the following command:

user@ desktop ~ $ realpath /dev/disk/by-partuuid/2fbab938-cc71-407a-996a-874d4486fca8                       
/dev/sde1

As you can see, /dev/disk/by-partuuid/2fbab938-cc71-407a-996a-874d4486fca8 actually points to /dev/sde1. That means my disk (“X”) is sde and my partition number (Y) is 1.

What this means in my case is that I would need to issue the following command to register systemd-boot:

sudo efibootmgr --create --disk /dev/sde --part 1 --loader "\EFI\systemd\systemd-bootx64.efi" --label "Pop_OS" --unicode

Notice how I filled in the e for X in /dev/sdX and 1 for Y.

After running the registration command, I get the following output:

BootCurrent: 0014
Timeout: 1 seconds
BootOrder: 0004,0003,0000,0015
Boot0000* Windows Boot Manager
Boot0001  Hard Drive
Boot0002  USB KEY
Boot0003* ubuntu
Boot000E  Hard Drive
Boot0010  USB KEY
Boot0015  Hard Drive
Boot0004* Pop_OS

Ignore all the weird device names, my motherboard injects those into the configuration. The important part is that my computer’s boot order is 0004 (Pop_OS), 0003 (ubuntu), 0000 (Windows Boot Manager), and lastly 0015 (a random hard drive). This is the order of bootloaders my computer will try before throwing up a “no bootable device” error. The asterisks next to the name indicate that they’re enabled somewhere in the boot order.

These numbers will look different on your computer. What you’ll probably want to do, is copy the bootorder as listed by the command that added the Pop_OS boot entry and add the number of your new bootloader in front.

Suppose I want to change my system to try to boot Pop_OS first, then ubuntu, then Windows Boot Manager. I can do that without booting into my BIOS through the following command:

sudo efibootmgr --bootorder 0004,0003,0000

You can pick any order, but I would advice not removing any unless you know what you’re doing.