I suffered from this a few months ago as well. The space and bandwidth flatpak was taking for about 2 small cli applications was obscene. Like 30gb all because it had accumulated about 10 nvidia drivers. I found the issue on github and it was closed as intended behavior. I install alot of rust apps from source and updating them from source was faster and easier than updating flatpak just due to the overhead of maintain those drivers.
That and the fact that every app has to be run through an alias or a. overly verbose command made me discount flatpak as a serious project. You can't ignore UX to that extent and just rely on technical merits.
The whole UFP thing is so wishy washy. It's such a broad category it is essentially meaningless, one of the earlier guardian articles talked about sliced bread being a UPF as it has added vitamins and minerals due to law.
If you closer at the whole topic it just comes across as saying if you are poor and eat food that you can afford you will die earlier. Writing a reminder of this on the food will not help anyone but it will make poor people feel a bit more like shit.