Are you tied to debootstrap or would multistrap also work for you?
I used multistrap to build the bootable sdcard image for odroid hc1. Also I used buster - so I'm not sure the same will work for you. But it might be worth a try?
For example this might be relevant:
...
-> apt install qemu binfmt-support qemu-user-static
...
* Next we need to configure all debian packages. This requires the use of qemu as emulator, if this step is run on a normal computer:
-> cp /usr/bin/qemu-arm-static /mnt/usr/bin/
-> mount --bind /dev /mnt/dev
-> mount --bind /proc /mnt/proc
-> chroot /mnt/ bash -c "DEBIAN_FRONTEND=noninteractive dpkg --configure -a"
* Likely this last step failed with a problen in the dash and bash packages. To work around it, run it once more with interactive dialoges:
-> chroot /mnt/ bash -c "dpkg --configure -a"
Above installs the qemu emulator so the desktop or laptop that you can use can run the arm binaries to perform a minimal configuration of the installation medium.
Good luck with your project!
Andreas