Here is the entire list for native on-prem PostgreSQL:
https://www.postgresql.org/docs/current/monitoring.html
And here are my favorites from that list.
PG_STAT_ACTIVITY – shows background activity for a running connection – not service by a connection pooler
https://www.postgresql.org/docs/current/monitoring-stats.html#MONITORING-PG-STAT-ACTIVITY-VIEW
PG_STAT_REPLICATION – the publication side view shows status of a publications subscribers – lag to them – must be queried from the publisher side
PG_STAT_ALL_TABLES – one row per table with summary use statistics
PG_LOCKS – the view that shows actively held locks – here is a post that creates a view from the most valuable fields in this view, and how to kill lock holders
Using RDS postgresql and terminating other processes
Progress Reporting – A whole set of views showing valuable progress information for an array of different PostgreSQL processes:
https://www.postgresql.org/docs/current/progress-reporting.html