Encrypted multiboot usb / adding cryptsetup to initrd

I'm trying to create a multiboot usb drive for Debian images including a live system, netinst, and DVD-1 iso. I've got as far as creating the partitions 1. EFI fat32 2. Boot luks2 3. ISOs luks2 Then I install grub targeting the efi and boot partitions, add a vmlinuz and initrd to the boot partition along with a custom grub.cfg. Grub successful unlocks the boot partition and then runs the kernel. However, at this point I can't get the kernel to unlock the ISOs partition where the iso images are. As far as I understand it, the initrd file downloaded from: https://deb.debian.org/debian/dists/bookworm/main/installer-amd64/current/images/hd-media/ does not include support for cryptsetup, nor does any other initrd image I've tried. It looks like I need to edit or make my own. My host system (also Debian) is able to unlock a luks partition so it is obviously possible, but I don't know the steps to take to set this up on a usb drive. My grub.cfg menuentries look a bit like:

# Workaround for "out of memory" error
rmmod tpm

menuentry "Install" {
   set isofile="/debian-${VERSION}-amd64-${installer}.iso"
   set options="cryptdevice=UUID=${cryptuuid}:luks root=/dev/mapper/luks quiet splash"
   linux /vmlinuz iso-scan/filename=$isofile $options
   initrd /initrd.img
}

menuentry "Live" {
    loopback loop ($root)$isofile
    linux (loop)/live/vmlinuz boot=live findiso=$isofile
    initrd (loop)/live/initrd.img
}

At the moment the iso-scan fails to find the iso image and it appears that the 3rd partition is never unlocked. I'm a little bit over my head with creating a custom initrd and am not sure where to start. A lot of the documentation assumes you are running commands on the local system for the local system. EDIT: I've had some success using debootstrap and then chroot, installing a few things and then using mkinitramfs, however it doesn't load properly > Gave up waiting for root file system device. Common problems: ... ALERT! /dev/mapper/luks does not exist. Dropping to a shell!