Hi Jim!
1. There shouldn't be any issue opening an account for US citizens, I know multiple who have done that, as long as you have an address where N26 operates.
2. The IDnow team will only verify your ID documents, they are not going to ask you any additional questions regarding residency, etc.
3. A lot of people are a bit "butt hurt" after N26 started charging _some_ fees. The main one being a 1.7% charge on ATM withdrawals outside of the Euro zone. And yes, when N26 got their own banking license, their customers obviously had to be moved over and get account numbers associated with N26 Bank, instead of their old partner, Wirecard. But you had a few months to move over (from early November to January), not 21 days. You had 21 days to activate your new card from when you ordered it, which seems reasonable. They also very helpfully provided you a list of "transaction partners", i.e. parties that had used to send you money in the past, so you could provide them with your new account numbers with ease. And your old account number would still work for a few months as a grace period.
You can read more about the changes here: https://nomadgate.com/the-n...
As for Deutscheskonto, my guess is that N26 suspended their affiliate partnership and that's why they so vehemently tries do not send any readers there anymore. It looks like they have replaced every single link to them with a DKB link, so that's quite telling.
Still, DKB is also a good bank. But I would only recommend it if you speak German (in my experience they refuse to communicate in English) and if you use it as your main account (i.e. deposit at least 700 EUR every month—otherwise they have quite high fees). And even if you do both of those things, N26 still has much better apps and online banking than DKB.
I don't think you can go wrong with either :)