IMO it's totally fine for buses to keep using ICE for many years to come. There are orders of magnitude fewer buses than cars, they are already pretty fuel efficient, and everything that makes public transport more expensive is very bad in my opinion.
If we had zero cars in a city, but 10k diesel buses, the city would still be better than if it had 100k cars and 500 electric buses. I'm making up these numbers, of course.
Point being: sure, electrify everything eventually, but let technology improve and let prices go down to the point that it makea sense for public transport.
Right now, an extra diesel bus would do more good than replacing a diesel bus with an electric one in many cities.
If we had zero cars in a city, but 10k diesel buses, the city would still be better than if it had 100k cars and 500 electric buses. I'm making up these numbers, of course.
Point being: sure, electrify everything eventually, but let technology improve and let prices go down to the point that it makea sense for public transport.
Right now, an extra diesel bus would do more good than replacing a diesel bus with an electric one in many cities.