To monitor SQL Server replication, you should first add in the custom metrics from this article: https://thwack.solarwinds.com/content-exchange/database-performance-analyzer/m/custom-metrics/3748. The custom metric queries are also attached to this article as well.
When adding the metrics, set thresholds on the ones you want to alert on, and then create a Resource Alert similar to below. To use a single alert for all replication metrics, choose All Metrics in a Category as the alert type:
I typically use an alert configuration similar to this:
