There should be a fast train between Berlin and Munich, but Google Maps does not reflect it in Schedule Explorer: best time us 4 hours.
A connection of less than 4 hours is only achieved when using the special ICE Sprinter connections. Compared to the standard connection, these trains skip some of the stops. They leave both Munich and Berlin around 6:00, 12:00 and 18:00. The precise times can be found in the table on this page.
Secondly, the search as you entered it in Google Maps suggests taking a regional train from Berlin Central Station to Berlin Südkreuz and only enter the ICE there. This doesn't make much sense as the ICE stops at the central station as well and pushes the travel time over 4 hours.
I suggest using the search at bahn.com instead. It's available in a couple of languages including English.
- I clicked the "Options" link and then checked the "trains" checkbox. This eliminates the distracting (and slow) bus trips from the search results.
- It's possible that that link will show you a different set of trains, since for all I know, it's looking at trains that leave "now", and you will click that link at a different time than I did, so the set of trains will differ.
- You may have to scroll through all the longer, indirect trips in order to see the short direct ones. I recommend that you click the "schedule explorer" link; that brings up a window in which it's (relatively) easy to scroll through the various options.