The rules are bewildering.
On Dutch NS trains, it seems, no ticket required if the bike is in a bag, disassambled.
But if that train plans to cross a border, then you get barked at. But maybe only if unbagged.
Returning to NL from Brussels, they wouldn't sell me a bike ticket, the checker didn't ask for one.
I'd like to take my bike on the Eurostar to London, but didn't see an obvious spot for it on those trains.
The Swiss trains all seemed to have bike hanging apparatus. But at the prices they charge, you may be better off hiring a private jet.