Is there any museum in Berlin that has a focus on Leni Riefenstahl's?
This is what I was able to find-- https://www.theartnewspaper.com/news/leni-riefenstahl-heir-donates-estate-to-berlin-museums
While not strictly a " focus " , The Film archives and museum in The Sony Center at Potsdamer Platz is a must . There is , as I recall , a section on Leni Riefenstahl . https://www.deutsche-kinemathek.de/en
I would search more for exhibitions than museums because for most museums (and the visitors) the topic is not of interest enough for a permanent exhibitions.