In many posts, we see people debating hiring a private driver, renting a car, or using other methods.
For my wife and I in the last 2 trips, the bus has been a good alternative. We took buses in Germany and Croatia. We have usually taken FlixBus, but there are others as well. We took the bus:
Frankfurt - Heidelberg - round trip
Cottbus - Dresden
Zagreb - Zadar
In these trips, the bus was quite comparable, or cheaper, than trains, and in some cases, the schedules were very convenient. Since buses are not confined to rails, they go to many towns that are not serviced by trains.
The buses were comfortable. In some cases, there were bathrooms on board. In other cases, there was a pit stop after 2 hours.
The buses are comfortable. They have been clean. In the US, the buses are taken by lower-class folks. In Europe, the demographic is a little higher.
So, my advice is to consider the bus as a viable, clean, and convenient alternative in many parts of Europe.