I have this exact dishwasher. To connect the app to it you have to go through a cloud account, but to its credit, you can turn the cloud connection off afterward and the app will then only talk to it through local wifi.
The dishwasher answers on SSH port 22. I suspect that the app's direct connection uses this and exchanges credentials via the initial cloud setup (so no cloud, no app connection either way).
I've found one useful feature not mentioned in the manual at all, that depend on the app: Popping the door open at the start of the drying cycle ("Efficient Dry" or something like that) vs. the end of it ("Auto Air"). Since changing this setting, plastic stuff is noticeably drier after letting it run into the night and then sitting open for the rest of the night. Stuff with higher thermal inertia (metal, porcelain, glass) is always dry except for the inevitable puddles at the top of upside-down mugs.
Actually I think you also need the app to run only the extra hot final rinse (for better drying) whereas "Sanitize" on the machine's UI runs the whole wash hotter.
The first thing it did after connecting it to the app/cloud was install a 70MB (!) software update. On a dishwasher.
Anyway I was not going to connect it to the cloud. But it flaked alarmingly. It would just sit there, blinking its red light, unresponsive to anything but power off, and there was no way to ask it what was wrong. Since the software update it has not done this, knock on wood.
The manual, btw, also doesn't mention this: If you do reset it via 4 second power button press, it does not go catatonic forever. It just sits there for 30+ seconds with all lights on and unresponsive. But then it does finish the reset. I'd previously run out of patience and unplugged it by then.
If you do RTFM you'll find that most of the features, e.g. how much rinse aid to dispense, are available through the machine's UI through deeply unintuitive keystroke sequences. But not all of them (like the mentioned delayed start).
I don't use the machine all that much, so a 20+ year lifetime is possible. Will the app and cloud still function then? I'd like to think yes - German companies are very customer service oriented. But we'll see. Whether the machine lasts that long and whether the app/cloud lasts that long. Keep in mind if you need the cloud to connect the app, you may have to do that every time you change phones.
One "feature" that this one has... with a 3:15h wash time (on the "auto" setting) it keeps things wet for so long that, say, rice starch comes off perfectly. On the previous, old, dishwasher it just got baked on really well by the hot dry cycle. Of course that dishwasher only took an hour, so you could run mutliple loads at the end of a big dinner evening. Win some, lose some.