Error: writing to file When using "official" chroot installation method

Im trying to install from a running Debian bullseye system and did the steps mentioned here:
Installing from Linux - NixOS Wiki (up to that point)

After calling NIX_PATH=“nixpkgs=channel:nixos-21.11” nixos-install --debug

The last thing that gets executed is

  • nix-build --out-link /mnt/tmp.2NrxdGFwaM/system --store /mnt --extra-substituters ‘auto?trusted=1’ ‘<nixpkgs/nixos>’ -A system -I nixos-config=/mnt/etc/nixos/configuration.nix
    these derivations will be built:
    [… 100 packages]

and then just fails with

error: writing to file: Operation not permitted

  • rm -rf /mnt/tmp.2NrxdGFwaM

I have no idea what file and what operation?

For testing I also copied /nix/store/ from the squashfs directly into /nix/store/ and then also
made it world rw, but apparently it’s some other file that’s not allowed?

Yes, I read the comment

Note that this may not work on all distributions (eg. older versions of debian stable).

But that’s what I have and no physical access to the machine atm, so no CD/USB method possible.