Originally “PC” was IBMPC or PC Compatible (as in compatible with IBM without using their trademark). An IBMPC could have run DOS, Windows or even OS/2

Brave calls itself a fork, which I suppose if its truly a fork, they are cherrypicking patches they can use from the chromium base, rather than recompiling with their own patch set on top

Not necessarily Apple being dominant, but the only thing that you need is a Web browser and no one will give a shit what you run that on, Windows, Mac, Linux, ChromeOS