Slow mode is not super useful but I found that some playtesters really liked it for precise angling in a certain part of the game, anyways on PS5 controller it should be the R1 button but I don't have a PS5 controller to test it with unfortunately
If you ever want to give it another try, I'll give you an hint for getting the other keys: try to think of rooms where the existing key could be "transformed"
Anyways I'm glad you enjoyed it!