I'm probably getting banned for committing this war crime but have you considered a

    #!/usr/bin/env -S bash -c "docker run --privileged ..."

    FROM docker
    
    RUN <<EOF cat >/other.Dockerfile
      #!/usr/bin/env -S bash -c "docker run ..."
      FROM debian:buster
    EOF
    RUN chmod +x /other.Dockerfile
    
    CMD bash -c "/other.Dockerfile &; ./main"