The information given loosely explains how to install rEFInd to the $ESP
on a fixed disk rather than a USB device. It was purely informational, after seeing comments that rEFInd is installed to a USB device, and also;
With the last comment I am in agreement. The information provided seems inconsistent. Nonetheless, I’ll add more information that might be useful.

I have replaced GRUB with the rEFInd bootloader, and it was installed on the external hard drive. Nevertheless, the problem with mounting the EFI partition persists.
If you did indeed replace GRUB with rEFInd, that is another issue in itself. Plus, as far as I’m aware, booting from a USB device isn’t a supported scenario.
Usually rEFInd is fully capable of chainloading most other boot loaders in your system, including GRUB, so, the typical scenario is to allow rEFInd to do just that.
If you have actually removed/replaced GRUB with rEFInd, it cannot.

I suspect there might be an issue with the partitioning or the mount options for /boot/efi, as this partition seems to fail to mount.
What specifically makes you think that? I ask because it could just as easily be an issue with GRUB.

As you can see, /boot/efi is located on /dev/sdb1
For the sake of clarity, /boot/efi
is a mountpoint to the EFI System Partition (ESP) ($ESP/EFI
) and not the partition itself. Call it the ESP… because, that’s what it is.

You mentioned restoring the boot loader, which is a possibility, but since I’m using rEFInd instead of GRUB, I wasn’t sure whether this applies in the same way.
This only enhances the reasoning for giving the information you queried; whether you use it, or not, is immaterial.

BootCurrent: 0008 Timeout: 0 seconds BootOrder: 0007,0002,0001,0000,0008,0009,0003,0004 Boot0000* Windows Boot Manager HD(2,GPT,32c5a3c8-fbf0-4ee6-a298-957aaa8a5053,0xc8800,0x32000)/\EFI\Microsoft\Boot\bootmgfw.efi57494e444f5753000100000088000000780000004200430044004f0042004a004500430054003d007b00390064006500610038003600320063002d0035006300640064002d0034006500370030002d0061006300630031002d006600330032006200330034003400640034003700390035007d0000006f000100000010000000040000007fff0400 Boot0001* manjaro HD(1,GPT,92ee68f5-5982-4269-8f18-930cc57625d8,0x28,0x64000)/\EFI\manjaro\grubx64.efi Boot0002* rEFInd Boot Manager HD(1,GPT,92ee68f5-5982-4269-8f18-930cc57625d8,0x28,0x64000)/\EFI\refind\refind_x64.efi Boot0003* Onboard NIC(IPV4) PciRoot(0x0)/Pci(0x1d,0x0)/Pci(0x0,0x0)/MAC(a4bb6d53e03e,0)/IPv4(0.0.0.0,0,DHCP,0.0.0.0,0.0.0.0,0.0.0.0)0000424f Boot0004* Onboard NIC(IPV6) PciRoot(0x0)/Pci(0x1d,0x0)/Pci(0x0,0x0)/MAC(a4bb6d53e03e,0)/IPv6([::],0,Static,[::],[::],64)0000424f Boot0007* rEFInd HD(1,GPT,92ee68f5-5982-4269-8f18-930cc57625d8,0x28,0x64000)/\EFI\refind\refind.efi Boot0008* UEFI: SanDisk PciRoot(0x0)/Pci(0x14,0x0)/USB(1,0)/CDROM(1,0x743260,0x8000)0000424f Boot0009* UEFI: SanDisk PciRoot(0x0)/Pci(0x14,0x0)/USB(1,0)/HD(2,MBR,0x0,0x743260,0x2000)0000424f
You appear to have two entries for rEFInd, and neither appear to be on the $ESP
of a USB device, as you claim. Which of these instances is working?
Judging by the file names, one is 64bit, and the other isn’t; of the two, the 64bit entry (specifying refind_x64.efi
) should be used. If working, this should be set as the default bootloader in your BIOS.

Boot0009* UEFI: SanDisk PciRoot(0x0)/Pci(0x14,0x0)/USB(1,0)/HD(2,MBR,0x0,0x743260,0x2000)0000424f
This Sandisk USB has an MBR
partition scheme, so it would be unable to boot a UEFI boot loader such as rEFInd in any case.
Additional;
MANJARO-REFIND-INSTALLER
A special Manjaro GUI application exists called manjaro-refind-installer which allows to specify the default kernel to use when booting from rEFInd:
sudo pacman -S manjaro-refind-installer
Despite it’s name, this package doesn’t actually install rEFInd, but it does offer a convenient GUI method to choose the kernel that rEFInd should reference to boot Manjaro via the kernel stub.
This may or may not be useful to you.
Overall, my opinion is that a fresh install might be in order. Please see links (below) in case they are useful.
Regards.
Ventoy A New Bootable USB Solution Boot with a Ventoy USB and ISO files are automatically listed in the Ventoy menu. Any ISO present can then be launched and booted directly. The obvious advantage here is that instead of constantly writing a Manjaro Installer ISO to a new USB any time you might need it, every ISO you desire can be stored on the Ventoy USB and launched the same way. A 32GB capacity USB would allow ample space to store several ISOs of your choice; an 8GB capacity USB might …
Multiboot Windows and Linux …on Separate Disks Firstly, this guide is intended for multibooting with each OS on a separate disk. If you have a laptop with only one disk, or If you wish to install an OS on it’s own partition on the same disk, this guide is not for you (but read on regardless, if interested). Secondly, this guide assumes each OS will be installed using UEFI and not UEFI’s CSM or Legacy mode. This guide does not support the traditional BIOS boot method. Additionally, all disks …