As @Soly said above, your best bet is to use Airtable’s DeDupe extension, which was specifically designed for these purposes.
That’s because there is no way to use Airtable’s API (via Make.com or other tool) to say “Search For All Duplicates”.
However, you can always custom-create your own scenario in Make to either:
(a) loop through all your records and then search on each record for more than one matching record.
(b) when a record gets created or updated in your Airtable system, do a search on that record for more than one matching record.
But again, it’s much easier to just use the DeDupe tool.