Paris and Berlin are now linked with an 8 hour daily rail service, that starts at €59. It produces 100th of the emissions of flying between the cities.
https://www.euronews.com/travel/2024/12/13/high-speed-train-from-paris-to-berlin-to-launch-this-winter-with-daily-connections-from-59
High-speed Paris-Berlin daily train service debuts

The route is the first directly linking the two capitals' city centres.

euronews
@ExtinctionR I note that it is direct to city stations not out of town airports so 8 hrs isn’t bad compared to train-fly-train. Also there are additional stops en route.
@markmason @ExtinctionR The additional stops are pretty minimal. Strasbourg and Karlsruhe are the two "last stations just across the borders" and Frankfurt you need for operational reasons (switching personnel).