From July 4, 2021, many of Berlin's museums will be participating in Museumssonntag (museum sunday). Which means, every first Sunday of the month, starting July 4, 2021, there will be no admission at numerous museums across the city. You can find a list of the participating museums here. The big museums on museum island are part of it for sure, but also many smaller galleries and exhibition sites.
See you there!
Bodemuseum, Museumsinsel Berlin, copyright: Staatliche Museen zu Berlin, David von Becker