I've travelled with a fully assembled bike on regional trains in Italy and it was pretty easy. I think technically they can say no if the train is especially busy, but mine never were. There was lots of space. Maybe even a dedicated carriage.
I've also travelled on these trains with a boxed bike, which was obviously no issue either.
The only downside was that these regional trains were a bit slower than the high speed inter city trains on which I think your bike has to be boxed.
I used the Deutsche Bahn app which has a box you can tick for bikes and filters the results accordingly. Not sure if it's still as effective as it was when I used it a while back.
I also once did Paris to Milan on a busy TGV with a boxed bike that ticked all the boxes in terms of what was allowed, but there wasn't really anywhere for it to actually go so the whole journey was mildly stressful.
I've travelled with a fully assembled bike on regional trains in Italy and it was pretty easy. I think technically they can say no if the train is especially busy, but mine never were. There was lots of space. Maybe even a dedicated carriage.
I've also travelled on these trains with a boxed bike, which was obviously no issue either.
The only downside was that these regional trains were a bit slower than the high speed inter city trains on which I think your bike has to be boxed.
I used the Deutsche Bahn app which has a box you can tick for bikes and filters the results accordingly. Not sure if it's still as effective as it was when I used it a while back.
I also once did Paris to Milan on a busy TGV with a boxed bike that ticked all the boxes in terms of what was allowed, but there wasn't really anywhere for it to actually go so the whole journey was mildly stressful.