Disable Secure Boot
When you want to permanently get back to a system without the Secure Boot stack, first disable Secure Boot in your firmware settings. Then you can disable the Lanzaboote related settings in the NixOS configuration and rebuild.
You may need to clean up the EFI/Linux directory in the ESP manually
to get rid of stale boot entries. Please backup your ESP, before you
delete any files in case something goes wrong.