Out of the box no Milestone XProtect server includes the ability to count people.
XProtect instead supports integrations implementing video analytics. There is a number of Milestone Solution Partners that offer video analytics including people counting.
If you have an XProtect System with an integration solution capable of people counting analytics you will most likely be able to pick up events or metadata using MIP SDK methods, how this can be achieved will depend on the video analytics integration.
You will be able to develop your own people counting video analytics and you will be able to use people counting video analytics developed by a Milestone Solution Partner.
You can search for solutions in the solution finder: https://www.milestonesys.com/community/business-partner-tools/partner-add-ons/
Please note the solution finder is not the complete list, there are integrations that are not mentioned..