Create one index that is partial, covering the movies rated 4.0 or higher; keyed on genre then release_year; and carrying title, so a query can read it from the index alone. Run VACUUM (ANALYZE) movies after creating it. Then explain two queries for genre = 'Drama' and release_year = 1981: one that repeats rating >= 4.0, and one that leaves it out.
Expected: the query with rating >= 4.0 gets an Index Only Scan on your index with Heap Fetches: 0. The query without it can't use the partial index and scans the table. If you skipped the vacuum you'll probably see a Bitmap Heap Scan instead, because an index-only scan relies on the visibility map that vacuum writes. Key order matters too: this index serves a query that fixes the genre and ranges over years.