They are weekday toggles per order type:

• Meal Prep Pickup Availability – days regular meal-prep orders can be collected. All seven days are shown (a code comment confirms this is deliberate: pickup availability is meant to be independent of the store's delivery days); new locations default to your account's own online-ordering days.
• Catering Pickup Availability (Catering module) – days catering orders can be collected; only days your account fulfils catering are listed.
• Realtime Pickup Availability (Realtime module) – days for real-time orders; only days your account allows realtime orders are listed.

If the delivery date's weekday is not ticked for the order type, the cart shows This pickup don't allow this day.