Quantum coherence is a real thing; "quantum activity" is not, except insofar as it is a very sloppy sort of shorthand for referring to quantum coherence existing at a macroscopic scale. (Put another way: my explanation of what was meant by this term was being incredibly charitable by presuming this was a good term to be using at all.)

If you look closely enough, everything is "quantum". Something being "quantum" is simply a matter of not being able to get away with using a simplification. I don't really see why that would matter.

Because macroscopic systems where you cannot get away with making this simplification exhibit really cool behaviors that can be exploited; superconductors are one such example, and quantum computers are (potentially) another.

That this question has nothing to do with consciousness is obvious.

I agree completely that it is not likely to be either necessary or sufficient for the brain to be a quantum computer to explain consciousness.