Does DPA track unused databases?

In DPA, you can easily create either a custom alert to notify you or if you want to view a time series you can create a custom metric.  

If you have a particular table, you could look at this older THwack blog article to create a custom alert if a table hasn't been updated. 

Alternatively, in SQL Server you could query the sys. objects table to find the objects that have changed and filter by modify_date and type ; U = User table, P = Stored procedure. Your query could return the count of the number of object that have changed and have it stored as a metric.   Alternatively, if you just want to do a quick check, you could go to the FINDSQL tab for a particular DB instance, set the filters to only include the particular database(s) and time range then search for UPDATE OR DELETE OR INSERT sql statements.

Hi jeff,
What about using the builtin command like sp_who (Transact-SQL) - SQL Server | Microsoft Learn ?

EXEC SP_WHO2