Since late 2020, the Admin Audit report includes this date point. But the customer needs to see this in the User Accounts report -- where it is most useful.
"We are trying to clean up accounts but do not want to accidentally delete new users."
Once the user creation date is visible on the User Accounts report, customers will
- see the "age" of each user alongside other values, and
- be equipped to filter-out newly created users, ensuring that new users don't get "cleaned up" by mistake
Without this column in the User Accounts report; the customer must download both reports (Admin Audit and User Accounts) for the same period and criteria, then import them into Excel, then try to meaningfully "join them together".