Day trip from Colmar to Freiburg with elderly person in August

I’ll be in Colmar in August and would love to take my (not so elderly but yet sensitive) father to spend a day in Freiburg, a city I adore. Since it will be August (the height of summer) I’m wondering if I should rent a car for the day. Would it be difficult to park outside the city center with a regular car (without an Umweltplakette)? Or would it be possible to take an Uber from Colmar to Freiburg and then another Uber from Freiburg back to Colmar? Would that be ok?

It would be so nice if there were direct public transportation connecting the two cities...

I’d really appreciate any help figuring out if this trip is possible.