Can I see a list of user name (Apple ID) conflicts?
Short answer: No
Apple does not provide a method to see a list of the affected accounts. The most you will get is the number of accounts that are affected.
Longer answer: You can work around this.
Google Workspace – If you have enough access to your Google Admin console, you can use the Reporting > Email Log Search option to search for the users that have received the email.
As of 2022-07-01, the message details to look for are
Subject: Update Apple ID