I haven’t tried it specifically, but it should work using the update record action in the automation. Just remember that if the text you copy into the linked field isn’t an exact match, then a new record will be created in the linked table. Also, sometimes ppl have trouble trying to do this when the primary key of the linked table is a formula. I was actually surprised that it could be done at all.
Yes, an automation can copy text from a text field to a linked field, thus creating the link between two records.
If the text field has commas, you may get unexpected results because Airtable will try to split the text into multiple records based on the commas.
If the text does not exist as a primary field in the linked table, and the primary field is an editable field, Airtable will create a new linked record.
If the text does not exist as a primary field in the linked table, and the primary field is a formula field, Airtable will not create a new linked record, because it cannot set the primary field.
If the text exist multiple times in the a primary field of the linked table, Airtable will not create a new linked record because it will not know which record to link to.
Another option is to take advantage of the new “find” action in Automations. Use the “find” action to find records that match the text field in the triggering record. Follow the “find” action with the “update” action, where you update the linked record field with a new list of the record ids found in the previous step. This will let you link multiple records that have the same value in the primary field. It will also let you link to records based on a field that is not the primary field.