config.scm:
--8<---------------cut here---------------start------------->8---
(operating-system
  ;; ...
  (bootloader (bootloader-configuration
                 (bootloader grub-efi-bootloader-removable)
                 (targets '("/boot1/efi"
                            "/boot2/efi"
                            "/boot3/efi"))))
  (file-systems (cons* (file-system
                         (device (file-system-label "boot1"))
                         (mount-point "/boot1/efi")
                         (type "vfat"))
                       (file-system
                         (device (file-system-label "boot2"))
                         (mount-point "/boot2/efi")
                         (type "vfat"))
                       (file-system
                         (device (file-system-label "boot3"))
                         (mount-point "/boot3/efi")
                         (type "vfat"))
                       ;; ...
                       %base-file-systems)))
--8<---------------cut here---------------end--------------->8---

/boot?/efi current state:
--8<---------------cut here---------------start------------->8---
oleg@guixsd ~$ find /boot?/efi -type f -exec ls -l {} \;
-rwxr-xr-x 1 root root 159744 May  8  2022 /boot1/efi/EFI/Guix/grubx64.efi
-rwxr-xr-x 1 root root 159744 Nov 16 04:28 /boot1/efi/EFI/BOOT/BOOTX64.EFI
-rwxr-xr-x 1 root root 159744 Mar 17  2022 /boot2/efi/EFI/Guix/grubx64.efi
-rwxr-xr-x 1 root root 159744 Nov 16 04:28 /boot2/efi/EFI/BOOT/BOOTX64.EFI
-rwxr-xr-x 1 root root 76 Feb  9  2020 '/boot2/efi/System Volume Information/IndexerVolumeGuid'
-rwxr-xr-x 1 root root 12 Feb  9  2020 '/boot2/efi/System Volume Information/WPSettings.dat'
-rwxr-xr-x 1 root root 129 Feb  9  2020 '/boot2/efi/$RECYCLE.BIN/desktop.ini'
-rwxr-xr-x 1 root root 159744 Nov 16 04:28 /boot3/efi/EFI/BOOT/BOOTX64.EFI
--8<---------------cut here---------------end--------------->8---

as you can see /boot?/efi/EFI/BOOT/BOOTX64.EFI is the thing needed for
boot, everything else probably a garbage.

mount points:
--8<---------------cut here---------------start------------->8---
oleg@guixsd ~$ findmnt  | grep efi
│ ├─/sys/firmware/efi/efivars   efivarfs                  efivarfs   rw,relatime
├─/boot1/efi                    /dev/sdc1                 vfat       rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro
├─/boot2/efi                    /dev/sda1                 vfat       rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro
├─/boot3/efi                    /dev/sdd1                 vfat       rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro
--8<---------------cut here---------------end--------------->8---

'/boot/grub' is not configured anywhere, but it's placed on a '/' mount
point which mounted from a raid disk array.