Welcome to the community, @Dani! :grinning_face_with_big_eyes: While you can’t use a formula function in an automation, you could create the value in another field and copy it over. For example, make a last modified time field that only tracks changes to that single select status field. Set up the automation to trigger on a condition: when that status field value changes to “Complete.” An “Update record” action would copy the date from the last modified time field—which would reflect the precise time that the change was made—to your static date field.
For the “Record ID” field, you’ll pick the ID of the record from the trigger step.
Record (from Step 1: ...) --> Airtable record ID
In the “Fields” section, you’ll select your date field, then fill that field (using the blue + button on the end) with the “Last modified time” field value from the trigger step.