Eu train companies should (according to EU policies) support one out of two open API standards (gtfs or netex), though they might be difficult to find.
There are a number of projecta that implement these, one of my favorites is https://direkt.bahn.guru/ which shows direct train connections for any (many/most?) European cities with the uae of DBs APIs (sadly it's currently down until new DB APIs are up again). Github: https://github.com/juliuste/direkt.bahn.guru
There is also the official EU night train map which I frequently use https://back-on-track.eu/night-train-map/
https://omio.com/ is pretty good as well.
3GPP has an interesting way of serialising bools on the wire with ASN.1
meaning only the type would be stored if true, otherwise it won't be set at all