I do not need to keep track of every time the Option A was selected. I only need to know if it was EVER selected. If it was selected once or many times, it doesn’t matter, there will be 1 log entry in the that history log field.
In this case, create an Airtable automation for that table, triggered by a record when it is modified.
If the single select is modified, run a Find on your History log table to see if that combination has existed before (X record, Y single select).
If it has, do nothing. If it hasn’t, create a record that links back to the trigger record, and states the select value it just changed to.
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Same premise for your linked record. Trigger am Airtable automation when it changes, create a new record in your history log with those details, linked back to the original trigger field.