Steps to reproduce:

1. Install postgresql 13 primary and standby instance ,add them with agent2 template
2. Navigate to items of standby host
3. Change filter to not supported
4. You will see Template DB PostgreSQL Agent 2: Replication: Lag in bytes not supported because received_lsn column changed to written_lsn in postgresql 13.
5. Also there is problem with item  Template DB PostgreSQL Agent 2: PostgreSQL: Get bgwriter: Checkpoint: Checkpoint sync time. in json sync_time called checkpoint_sync_time. But it can be channed in template, just updating you..

Result:
See screenshot...

Expected:
Replication lag work with postgres 13