I got my first look at BER about a week ago. I arrived on Friday and departed on Tuesday. The airport looks great and is named after former Berlin mayor Willy Brandt who, by the way, had no objection to the "ein" in "Ich bin ein Berliner" when JFK ran his speech by him before it was delivered at Rathaus Schöneberg in 1963 (but I digress).
I arrived from Frankfurt on a Lufthansa flight. The jet bridge was surprisingly steep. I wondered how well people with mobility issues could negotiate it. Since I arrived from Frankfurt, I did not experience immigration at BER. I wandered around the airport a little before heading into the city. There is an enormous mall-like area between the A gates and B gates in Terminal 1. The WCs in the B gate area were overflowing with people when I arrived, so I had to seek a WC in the A gate area. After that, I followed the signage to baggage claim.
Finding the S
There is an S line that goes to the airport (along with some regional trains), but the signage to get to the trains (especially the S) isn't very good. It took effort to find the S track, and it was found only after following the train signs out of the building, seeing entrances that went down to the regional train tracks (but not the S), staring intently at a "Your are here" type sign for a couple of minutes, and then hoping for success as I re-entered the building. There success was found. To avoid wasting time like me, follow the train signs, but make a left turn immediately before exiting the building (at the end of a divider/wall) and then go back in the direction you came from to get to the S.
Interestingly, there was a wide flight of steps that went down to the S station and only a single narrow escalator coming up. I watched several people struggle down the steps with large pieces of luggage. The ride to my stop -- the Zoo station in Charlottenburg (former West Berlin) -- took about an hour. I purchased my ticket on the BVG app (app for Berlin's transportation company). You cannot create an account on the BVG with a US address, so I use my B&B address. I find the BVG app pretty useful for buying tickets.
I returned to the airport for a 6:45 am flight on Tuesday morning amid stories of needing to arrive 4 hours before departure time. I arranged for a 4:30 pick up at my B&B; a car ride is less than 30 minutes instead of > 1 hour on the S. I was out front at 4:20 am, as was my driver. I was at the airport by 4:50 and was at the gate munching on a sandwich prepared by my kind B&B owner at 5:20 am. The airport was surprisingly busy at 4:50 am. I've found even most major airports to be pretty sleepy at that hour, but not BER. The ticket counters are laid out a lot like those at Frankfurt. The queue for the Lufthansa counter assigned to my flight was crazy; I was certainly glad to have no bag to check and to have a boarding pass on my phone. There was a decent (but not unmanageable) queue at security.
Passports, COVID, etc
Of note, I never showed a passport or other ID anywhere in the airport to get on my flight. I scanned my boarding pass to enter security and scanned it again to get on the plane. That was it. Also of note, my ticket only went to Frankfurt, so no passing through immigration. Also, nothing was required with regard to showing immunization or a negative COVID-19 test for flying from Berlin to Frankfurt.