seems resolved; what worked is:
xhost +
docker run --net=host --runtime nvidia --rm --ipc=host -v /tmp/.X11-unix/:/tmp/.X11-unix/ -v /tmp/argus_socket:/tmp/argus_socket --cap-add SYS_PTRACE -e DISPLAY=$DISPLAY -it nvcr.io/nvidia/deepstream-l4t:5.0.1-20.09-samples
deepstream-app -c /opt/nvidia/deepstream/deepstream-5.0/samples/configs/deepstream-app/source1_csi_dec_infer_resnet_int8.txt