Is frozen pizza ultra-processed?

It depends on the pizza, and unusually the base is rarely the problem. A dough of flour, water, yeast, oil and salt is group 3, and so is passata and so is mozzarella.

A plain margherita made from those three things is group 3, and a few genuinely are. Freezing changes nothing, since it adds nothing.

The toppings are what move it

• Processed cheese or a cheese blend with emulsifying salts, which is common on cheaper pizzas: group 4.
• Pepperoni, ham and most cured toppings, which are usually reformed with stabilisers: group 4.
• Dough conditioners and emulsifiers in the base, common in thin and crispy: group 4.
• Flavourings in the sauce: group 4.

The same split runs through cheese and sausages generally: whether the dairy and the meat are the things themselves or reformed versions of them.

Working this out from a receipt is harder than from a packet, because a till prints about twenty characters of product name and no ingredients list. That is the problem Bagged exists to solve, and how a receipt is structured explains why it is the hard part.