Welcome to the Airtable community!
It is not possible to disable selection of a particular single-select value based on what other people have signed up for.
You can, however, create a system with linked records, rollups, and filtered views to avoid having too many people sign up for the same type of dish.
Create a table with a row for each type of dish (main dish, dessert, side, etc.). Indicate the maximum number allowed in a number field. Have each form submission include a linked record field that links to the table of possible dishes. Use a rollup field to determine how many people have already selected that type of dish. Compare the number of submissions with the maximum number allowed in a formula field and use that result to create a filtered view that excludes dishes that have been maxed out. In the table for the form, limit selection of records to that filtered view.
Whew, that sounds like a lot and depending on your level of experience with Airtable might be too much or not enough info. Sorry, I don’t have time for a full write-up right now.
