I have travelled extensively by train in Europe for years. I can’t recall seeing a set belt.
The one time I did see people sitting in the aisles of an overcrowded train was out of Fankfurt. Spring break had just started and kids were headed to Britain. The train was so crowded that my wife and I could not get to our first class seats. I sat in the aisle on our luggage.
During that trip we never saw anyone to check our tickets and border customs did not bother to check passports on the borders.
Not and unusual occurrence when posting out of my posterior.