SQL Server mirroring for more than 10 databases
Database Mirroring is a legacy technology that has been superseded by AlwaysOn Availability Groups


  Maximum number of availability groups and availability databases per computer: 
  
  The actual number of databases and availability groups you can put on
  a computer (VM or physical) depends on the hardware and workload, but
  there is no enforced limit. Microsoft has tested up to 10 AGs and 100
  DBs per physical machine, however this is not a binding limit.
  Depending on the hardware specification on the server and the
  workload, you can put a higher number of databases and availability
  groups on an instance of SQL Server.


Prerequisites, Restrictions, and Recommendations for Always On availability groups