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CMS Meta Tags Fields only a few options not including the field i want

Hey guys, trying to add SEO tags for some recipes on a site and I am only getting a few fields as options to add to the meta description but not the field I want to add. How do I add a different field?

Does anyone know why only some fields are available in the collection meta description? I would like to have my main description fill out the META tag if possible but it is not an options (maybe too long?)