This pile of garbage will so SSM RDP on a Mac if you have the aws-cli and Microsoft RDP client installed. I'm not proud of this but it was useful to me.

ssm-rdp.sh

#!/usr/bin/env zsh -e
LOCAL_PORT=$(( $RANDOM + 32767 )) # Handily $RANDOM gives a number between 0 and 32767, so this will give us a random port between 32767-65535
REMOTE_PORT=3389

target_id=$1

aws ssm start-session --region eu-west-1 --target "${target_id}" --document-name AWS-StartPortForwardingSession --parameters "localPortNumber=${LOCAL_PORT},portNumber=${REMOTE_PORT}" &
SESSION_PID=$!
RD_TEMP=$(mktemp -d)

tidy() {
  [[ -d $RD_TEMP ]] && rm -rf "${RD_TEMP}"
  kill ${SESSION_PID}
}

trap tidy EXIT

> ${RD_TEMP}/ssm.rdp <<EOF
full address:s:127.0.0.1:${LOCAL_PORT}
prompt for credentials on client:i:1
EOF

sleep 5

open -F -W ${RD_TEMP}/ssm.rdp