There is currently petition citizen initiative underway to urge the European Commission to connect all capitals of the EU with high-speed rail.
I’ve already signed it, are you joining ?
https://europa.eu/citizens-initiative/select-language?destination=/initiatives/details/2023/000004
Edit: It’s not a petition, it’s a citizen initiative.
If you’re interested in EU cross-border rail connections, I highly recommend following Jon Worth on Mastodon. He spends a lot of time actually testing the various border routes (and has some pretty strong opinions on them).