In December I could not even buy tickets online to a train from Berlin to Warsaw because DB website is terrible. Had to cancel my trip — this is really a shame, that EU cannot fix cross-border connectivity.
https://www.seat61.com/trains-and-routes/berlin-to-warsaw-by...
The EU seemed (2021) to be working on it https://ec.europa.eu/commission/presscorner/detail/en/qanda_...
Apparently, railway companies cannot make sites.