Such an exaggeration. >92% of the area is served with 5G. Calls are available in 98%-99% of the area (though sometimes just from one of the operators). Some trains were built in a way that blocks reception, though those have had repeaters or wifi for a while. I know plenty of people who work from the train every day.
Sources:
https://www.bundesnetzagentur.de/SharedDocs/Pressemitteilung...
https://www.bundesnetzagentur.de/SharedDocs/Pressemitteilung...
https://de.wikipedia.org/wiki/Intrain-Repeater
https://www.heise.de/en/news/Mobile-communications-for-rail-...