Deactivate option if selected once - #4 by LN is where we discussed this last. The schema that was last saved could possibly be incompatible with a query in the form but in that case a blank value would be returned. We'll try to schedule this one soon.
This would require some preprocessing of forms that's not currently done.
As of Collect v2024.1, last-saved values are kept across form updates. We are not currently planning to store last-saved values for encrypted submissions.