All that would be needed is an 8bitdo adapter to connect the DualSense to a Nintendo Switch. MidnightMan, content creator, showed in his unboxing video that the PS5 controller is recognized by the PS4 although it is unusable on this platform, except in remote-play. However, the controller will be usable on PS3 with the help of a simple cable.
Note that the DualSense won't have access to all its features on these platforms and will be limited to its basic functionalities.
Original content by Xaleo.