Pennyworth is about Batman's butler, Alfred Pennyworth, in his younger days.
It seems like an odd mix of time periods. 1960s clubs and cars, music from the 70s and 80s, public executions from the 1800s, airships from the 30s.
More random details: Cliff Richard and The Shadows breaking up is current news (1968) but also the Reich is apparently still a thing (1930s).
When is it supposed to be set?