Museum Berlin Karlshorst - the closest thing to a must-see. We really enjoyed the Surrender Museum in Reims, and would like to see
this one.
This was an important place for me to see on my first trip to Berlin, and it was a very worthwhile activity. While the museum is great (including the room where German's military leaders surrendered), it is also nice to see the Karlshorst neighborhood, which began being built in 1895. For an excellent memoir that shows the life of a child in Karlshorst pre-war (and follows the author's life into WWII and post-war Germany), see Joachim Fest's excellent Not I: Memoirs of a German Childhood.
> Platform 17 Memorial
This is another site that was important for me to see on my first trip to Berlin. If you happen to have interest in Dietrich Bonhoeffer, his parents' house (which was also his home while in Berlin and the site of his arrest) is a 30-minute walk away. This walk also passes through a gorgeous neighborhood built in the early 1900's; picture perfect gardens are all along the way. The Bonhoeffer Haus is typically open on Saturday mornings, but there is a mechanism for private appointments if you can't make it on a Saturday (which you can't). A tour includes a viewing of Bonhoeffer's bedroom with some original furniture. https://www.bonhoeffer-haus-berlin.de/
> Nazi Forced Labour Documentation Center
This is a new one for me. I wasn't aware of its existence. This looks like a good one.
> Soviet Memorial in Schonholzer Heide and/or Soviet Memorial Treptow
Both memorials are interesting, but the Treptow Park memorial is more impressive with its ENORMOUS sculpture of a Soviet soldier holding a German child while his feet stand on a crushed swastika. The Schönholzer Heide memorial is also very worthwhile to see, but (1) with your time being short and (2) with the ease of combining a Treptow Park visit with The Nazi Forced Labour Documentation Center visit (on the same S line), I would probably just do the Treptow Park Memorial.
> Alter Garrison Friedhof and/or Invaliden Friedhof
This would not be high on my list of places to see during my first visit to Berlin, but you may value this more highly than I.
> Militarhistorisches Museum
I'm assuming this is the museum at Gatow Airport. If so, it is a good museum. It is in the middle of a re-working of the museum; the former exhibit in one of the hangars regarding the Berlin Airlift from 1948 to 1949 appears to be a victim of the re-. To me, the Berlin Airlift is one of the US's greatest moments, and I am a particular fan of Gail Halvorsen, the US pilot who began dropping candy to Berlin's children during his flights into Tempelhof Airport. The airport was greatly expanded by the Nazis; it was their central airport for Berlin; and it was the central airport for the Berlin Airlift. A critical place for me to see during my first visit to Berlin (and well above the Gatow Museum) was Tempelhof Airport and the nearby Berlin Airlift memorial. There are 2-hour tours of the airport, if this is of interest to you -- https://www.thf-berlin.de/en/your-visit/guided-tours.
> German Resistance Memorial Center
Good museum. The entrance is off the courtyard where Claus von Stauffenburg was executed after the failed Operaion Valkyrie assassination attempt on Hitler.
The Humboldthain partially-collapsed flaktower is cool, and it can be combined with the Berliner Unterwelten Darkworlds tour, which takes visitors into a a WWII bunker for citizens of Berlin (https://www.berliner-unterwelten.de/en/guided-tours/public-tours/dark-worlds.html). BUT your schedule is already quite full.
I hope that helps -- and I hope it is not too much information.