The whole idea of ultra-processed food seems to be mostly political. The original paper from Brazil was written by left-wing academics (and for the record, I am a fully paid-up Guardian reader). One of the criteria for seeing if a food is a UPF or not is whether it comes from a multinational company. Apparently knock-off own-brand Oreos are less bad for you than ones made by Mondelez.
But if you take the original definition of processing seriously, almost every manufactured food item is a UPF. Partly this is because they only have three categories: Unprocessed foods (an apple), minimally processed foods (an apple cut into slices and sold in a little bag for kids to eat, although obviously not as part of a Happy Meal at McDonald's, good god no, and won't somebody think of all the plastic), and the rest is ultra-processed. So for example one of those nice small-batch deep-frozen ready meals you can get at the farm shop is ultra-processed as much as a £1.95 chicken'n'rice thing from Iceland.
To give another example, is a portion of chips (potatoes cut up and fried in vegetable oil) minimally processed or ultra-processed? It doesn't seem like a lot of processing to me. Maybe an intermediate category is needed, "More than minimally- but less than ultra-processed" foods.
This leads to problems for the people who take the UPF story politically, because obviously Coco Pops are bad (high in sugar, made by an American company and OMG don't get me started on that company's founder's attitude to masturbation) whereas obviously artisan sourdough is good. So artisan sourdough is now classed as a minimally processed food because nice enlightened people eat it, unlike those poor plebs who eat Kingsmill, even though it has been processed from raw wheat every bit as much. If the UPF thing catches on, there will probably be demands for labelling, and then the process of gaming that can start too. And guess what, the multinationals always win those, because Iceland and Mondelez can buy more politicians' attention that your farm shop's small-batch supplier.
As @IcedPurple says, in some ways this is all just a repeat of existing advice anyway. I don't see much difference between the UPF thing and the "eat your five-a-day", "get more fibre", etc, movements. George Orwell was writing about the tendency of the middle classes to scold their social inferiors for this in 1937 in "The Road To Wigan Pier":
"The basis of their [a unemployed miner's family] diet, therefore, is white bread and margarine, corned beef, sugared tea, and potatoes – an appalling diet. Would it not be better if they spent more money on wholesome things like oranges and wholemeal bread or if they even ... saved on fuel and ate their carrots raw? Yes, it would, but the point is that no ordinary human being is ever going to do such a thing. The ordinary human being would sooner starve than live on brown bread and raw carrots. And the peculiar evil is this, that the less money you have, the less inclined you feel to spend it on wholesome food. A millionaire may enjoy breakfasting off orange juice and Ryvita biscuits; an unemployed man doesn't. ... When you are unemployed, which is to say when you are underfed, harassed, bored, and miserable, you don't want to eat dull wholesome food. You want something a little bit 'tasty'. There is always some cheaply pleasant thing to tempt you. Let's have three pennorth of chips! Run out and buy us a twopenny ice-cream! Put the kettle on and we'll all have a nice cup of tea! ... White bread-and-marg and sugared tea don't nourish you to any extent, but they are nicer (at least most people think so) than brown bread-and-dripping and cold water. Unemployment is an endless misery that has got to be constantly palliated, and especially with tea, the English-man's opium. A cup of tea or even an aspirin is much better as a temporary stimulant than a crust of brown bread."
The net result of all this is to further stigmatise people who eat convenience foods, rather than allow us to question what it about our society that leads to demand for those foods (such as, cooking and shopping take a fuckload of time, and we don't have that because we're working so hard).
Relatedly, we're not even really sure how bad most of these UPFs are anyway. Nutritional epidemiology continues to be a total mess. The researchers might know that people who say they eat their five-a-day live longer, but they don't know how much of that is because of the food and how much is due to other factors that make you better at getting your shit together to eat your five-a-day. Everyone is looking for "the next tobacco", the next thing that will magically fix obesity and early death, and it may not exist. But in the meantime there are pages to fill and breakfast TV shows to be gone on and clicks to be had and merch to be sold.