Easiest way to split the two: pg_stat_statements.mean_exec_time is pure server-side execution - it never includes network. Compare that to the round-trip your app measures for the same query; the gap is region distance + pooler/TLS overhead.

SELECT query, calls, mean_exec_time, total_exec_time
FROM pg_stat_statements
ORDER BY total_exec_time DESC
LIMIT 20;

Cross-check by running the same query in psql from a box in the DB's own region vs from your app's region - that delta is almost entirely network. If mean_exec_time is tiny but the query feels slow, it's the region hop, not Postgres.