Does macOS 11 Big Sur support FireWire?
FireWire support, in general, has not been removed from macOS Big Sur or Apple Silicon.
This video demonstrates daisy-chaining 3 FireWire peripherals to an M1 MacBook Pro running macOS 11 Big Sur:

FireWire Hard Disk
FireWire Audio Interface
FireWire Video Camera


So all-in-all I'm really surprised all this equipment still works, or at least it works the same way as it did in the previous versions of Macs with Intel processors.
I honestly expected Apple would have dropped FireWire support on these newer Macs but, surprisingly, it's still possible as long as you have the right adapters.
https://www.youtube.com/watch?v=x5ISyI3VcWo