Update: Ha Ha!! Never fails, as soon as I post to GeoNet I figure it out. Well, maybe not figure it out, but flail around long enough for something to work. One difficulty is that the user name associated with Pro is not the same as what I use for our Enterprise Login, or perhaps the second part of it is hidden and automatically supplied when logging in, so the actual user ID we enter is different.
Original question: Our institution recently switched to single sign-on, requiring everyone to create a new account. Our old content had to be manually moved to our new accounts by the administrator. But my problem now is that when I try to share items from Pro, I'm not given the option of using my new account. How can I get Pro to acknowledge my new account?