Driving in Europe with a U.S. registered vehicle is NOT prohibited. However, only vehicles that will only remain in the country for under 6 months can be driven without registration in Europe. Any vehicles that will remain in the country permanently or over the 6 month timeframe must be registered before it's too late.
https://www.shipoverseas.com/blog/2014/02/04/road-trip-from-usa-to-europe-how/