It appears docker rmi $(docker images --quiet --filter "dangling=true") for the built in delete_dangling_images script has been depreciated (or at least has changed.) I updated the script to this below and it works well (I also added a few checks and prune the volumes too.) I read that some applications with older "data container patterns" could be inadvertently destroyed using this method but it did not affect any of my many containers. Maybe someone knows more about that.
/boot/config/plugins/user.scripts/scripts/delete_dangling_images/script
#!/bin/bash
#arrayStarted=true
#noParity=true
echo
echo
echo Removing unused images...
docker image prune -f
echo
echo
echo Removing unused volumes...
docker volume prune -f
echo
echo
echo Finished
echo
echo
echo ...If 0B shows above, no dangling images or volumes were found to delete...