Airtable deals with record uniqueness under the hood using a randomly generated record ID. You can see this ID using the
RECORD_ID() function in a formula field. Aside from that, it doesn’t prevent the creation of records with the same data in the primary field, nor does it provide any mechanisms for alerting the user of such duplications. It’s possible to run an automation on a schedule that executes a script to look for and mark records with duplicate primary field values, but this will obviously eat up a lot of automation runs depending on the schedule chosen.
What method are you using to create the primary field contents? If it’s a formula, the best solution there is to add as much unique data as possible to the formula’s output so that you effectively guarantee unique values, although doing so obviously makes the field contents longer and not as easily consumable at a quick glance.
In lieu of running an automation on a schedule, you might consider manually running a script periodically to look for and mark records with duplicate primary field content.
Another option is to use the Dedupe app to find duplicates, keeping in mind that it’s also designed to delete and/or merge duplicate records. You could just skip that part and use it for review only.