When a group restricts categories, Category Union decides how a meal must match them. The chosen categories are first split by category group (e.g. Diet: Keto, Paleo; Meal type: Lunch):

• And — a meal must match every selected category within each category group it is tested against.
• Or — a meal only needs to match at least one selected category, in any category group.
• Auto — a meal must match at least one selected category in each category group you restricted (a middle ground: partial match is fine within a group, but every restricted group needs a hit).
• System Default — falls back to the store-wide Meals Filtering setting (Client Config, Business: General tab), which itself offers AND / OR / Default.

If customers in a group see no meals at all, the restriction is usually too strict — switch to Or or remove categories.