Although tickets for Bundesliga games include 'free' travel within the respective geographic regions concerned, it's possible to purchase from the Bundesbahn (German Railway System) a ticket for the princely sum of 9 Euros, which offers unlimited travel throughout Germany for the whole month of August* as long as you travel on local/regional trains.
*The Bundesliga season starts on 5 August. See
https://tinyurl.com/ywna7rmr for the fixture list.
Ticket details:
https://www.bahn.com/en/offers/regio...euro-ticket-en
I will be over there for a week and will take in a Union Berlin game in passing.