Explanation
Salesforce Authenticator is an app that adds an extra layer of security for logging into Salesforce by requiring users to verify their identity using their mobile device after entering their username and password on Salesforce login page. To see how many users have successfully used Salesforce Authenticator since it was rolled out, an administrator can use two methods:
A) Create a new view In Identity Verification History, specifying Method.
Identity Verification History is a tool that shows information about each identity verification event for users in your org, such as the date and time, the verification method used, the IP address, and the status of the verification. By creating a new view in Identity Verification History and specifying the method as Salesforce Authenticator, an administrator can see how many users have used the app to verify their identity when logging in. References:
https://help.salesforce.com/s/articleView?id=sf.identity_verification_history.htm&type=5 D) Export Login History and filter based off of Authentication Method Reference.
Login History is a tool that shows information about each login attempt for users in your org, such as the date and time, the username, the source IP address, the login type, and the status of the login. By exporting Login History as a CSV file and filtering based on the Authentication Method Reference column, an administrator can see how many users have used Salesforce Authenticator as their authentication method when logging in.
References: https://help.salesforce.com/s/articleView?id=sf.monitoring_login_history.htm&type=5

A custom summary formula is a formula that calculates values from summary fields in reports such as sums, averages, counts, etc. Custom summary formulas can use functions such as PREVGROUPVAL which returns the value of a field from the previous row at the same grouping level. By using a custom summary formula with the PREVGROUPVAL function, an administrator can create a report to calculate the year-over-year change in the dollar amount of a company's opportunities by subtracting the amount from the previous year from the amount from the current year and dividing by the amount from the previous year. References:
https://help.salesforce.com/s/articleView?id=sf.reports_builder_summary_formulas.htm&type=5 https://help.
salesforce.com/s/articleView?id=sf.reports_builder_functions.htm&type=5