Hey Julia! 👋 Abby here from the mixpanel team. The fastest way to set this up would be to create a new insights report, and in the query builder select "all events" and Unique Users. Then, above the report itself, select "Month" as the increment and you should get unique users who performed any event in a given month.
as you change your metric for "active" over time (i.e., it's users who perform some subset of events, not any event), you can create a custom event and use that instead.
