Azure DevOps extract unique visitors
I don't know of a built-in way but here are two hacks:

You can look at https://dev.azure.com/{organization}/_settings/audit , then set the date range to what you want and manually count.

An automated way of doing that could be to use the ADO REST API and send a Query to get the Audit log, then use a bit of code to tally up the unique users from the response.