My personal experience is that on ICE trains (i.e. long distance travel) nearly everyone wears an FFP2 mask for the entire journey except when eating, whereas people take a few more liberties on the regional trains.

Here in Berlin things were getting slacker on the U-Bahn recently, but coverage of the fourth wave seems to have had an effect - on several U-bahns today FFP2s were universal apart from the odd jakey.