It really is nonsense when people try to define it scientifically.
This is the closest to anything we found that makes sense https://en.wikipedia.org/wiki/Food_processing#Processing_lev... but it's kind of separate from the popular idea of processed foods
Here's a Nature article discussing the problems: https://www.nature.com/articles/s41430-022-01099-1
It's likely just my biases but I've noticed that the vast majority of people using these nonsense terms are, hmmm, let's just call them high calorie humans. They really want to believe
Of course the lists of regulated chemicals and all the weird stuff it covers are don't correspond to what anyone imagines "organic" means, but it is not marketing puffery.
I dunno about you, but this definition doesn't seem to work for me.
Orange juice has gotten sweeter, even shop bought blackberries are noticeably worse than wild blackberries so I just dont buy the fruit and veg now.
Naturally ripened bananas taste so much better than the artificially ripened bananas and you can taste the gas used to ripen the bananas even though they claim you shouldn't be able to.
Carrots today are horse stock carrots, big, bland and no taste. Spuds, you cant get a decent baker with a decent skin on it any more, come back Spud U like, all is forgiven.
The mince meat from supermarkets is just gristle that leaves feeling worse for wear.
Yoghurts, massed produced sludge, designed to forced through pipework for automated containerisation.
Successive Govts have allowed this to occur in the UK and then they wonder why the NHS cant cope.
Thing is, for most people they havent noticed this decline in quality food so they think you are nutter when you complain about the decline, which probably explains the rise of the influencer.
Cheap crap food masks the costs to your health.
I think you're right about steaming though, if you're going for maximum nutrition you're better off eating some vegetables raw.
The ultra-processed food are not nonsense, only hard to define depending on your culture.
One example my sister used is bread.
If your bread contain flour water and salt, it's processed food but not ultra-processed. Everyone agree. Even if you use multiple different flour and nuts, still the same.
After that, you can add oil on the bread before cooking it (not mixed with the bread,just on top, to change the crust formation). It is possible to consider it ultra-processed now (people rarely do, even in France).
Now come the question of sugar (there is a salt question too but I don't know enough to talk about it). Sugar help conserving the bread. In France, some people (including me) consider that any amount of sugar in bread makes it ultra-processed. Some consider that it only is if the bread cannot be just called bread, but that depends on your culture. Some 'bread' in the US would be called 'brioche' here by almost everyone.
But for the majority of stuff, it's easier : if it's a pre-prepared meal with conservatives, it's ultra-processed.
Which does not mean it's bad, though. Generally it is, but not always. Nutri-score (at least the last iteration, the previous one was flawed against fat in general and insaturated fat in particular) is imho a better way to look at food.