that firmware version is out-of-date… probably why you are having this issue. try rebooting your hub to see it is contacts the ST servers and attempts to download the latest version. watch the led colors on the hub after rebooting. if still on 46.x, you should contact ST support.
firmware 49.9 is the latest… https://status.smartthings.com/incidents/jgf5d78p7nbm
Thanks so much for the observation / information and recommendation.
I power cycled my hub and noted the reported firmware shortly after rebooting matched the latest (49.9).
I then tried to open a commissioning window again from the Alexa app and this time SmartThings was successful in the iCloud step as well as adding the device to my setup.
It seems to be working!