I'm British but I always understood it as the second meaning. e.g. "We were going to consider XYZ but now it's a moot point because the project is cancelled."

I've heard it used that way in the UK too, but the first meaning is traditional. Wiktionary has some examples:

https://en.wiktionary.org/wiki/moot

I expect the US meaning will eventually become standard everywhere.

It sort of means both simultaneously, doesn't it (we could discuss it but it's inconsequential), but we do tend to use it in that formulation most.