Postgres index usage

I've found multiple postings out there saying you can query pg_stat_all_indexes and look at idx_scan to know if an index has been used by queries. I want to be 100% sure I can rely on that table/column to know if an index has never been used.

I queried that table for a specific index and idx_scan is 0. I queried pg_statio_all_indexes and can see idx_blks_read and idx_blks_hit have numbers in there. If the index is not being used then what it causing idx_blks_read and idx_blks_hit to increase over time? I'm wondering if those increase due to DML on the table. Could anyone please confirm I can rely on pg_stat_all_index.idx_scan to know if queries are using an index and the increases over time in idx_blks_read and idx_blks_hit in pg_statio_all_indexes would be from DML (or possibly vacuum or other things)?

Thanks in advance.
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