I didn't encounter any issues, the majority of pavements have low edges to go up and down, I used both the buses and U-bahn without difficulty, everyone was extremely helpful. We visited the Reichstag building and I was able to take my mobility scooter in a special entrance with no problems at all, everywhere we visited they did their upmost to accommodate us one way or another.

Some road crossings didn’t have drop kerbs but the majority did, and overall the city was accessible

In the BVG app you can search for barrier free public transport options.

The part of East Berlin where we stayed was older and did not easily accommodate a wheelchair. The most difficult problem was getting on and off the trains, because of the distance and different elevation from the train to platform. The public could not have been more helpful. I could walk with the use of a cane for short distances, which helped to accommodate my needs.