Validating tickets thankfully isn’t a problem any more. Most people have the Deutschlandticket now, so you can just jump into any regional train or bus without any problems. ICE and IC tickets also don’t need to be validated and are digital more often than not.

I’m an American and went to Cologne a few years back for Carnival. Flew into Frankfurt Airport, the train was right there and I was at my destination in about an hour traveling along a scenic river. Absolutely amazing!