There should really be an "IF" statement that if it isn't empty use the 2 values with the comma. If it is empty only use the new value. That way you don't end up with random commas. (Not sure you would but it is a more defensive way to code it.)
hi @Gargazaur , I would use an automation.
fields: linked records of studies, linked record of new study to add.
Automation: When field new study to add is updated, update the same record using the old values of linked records of studies and the...
You can do this natively in Airtable. You were close with your idea but don't need a script. Have a text field for that record. When the text field is updated, copy the text field into the single select field. That will create the new option.
