Pretty sure there are lots of valid definitions of "cross-platform", and I will say again that context matters.
If I'm talking about a mobile app and I say "cross-platform" I probably meant iOS and Android. It would be strange to say "what about Linux??" in that context.
So here we are talking about competitors to Adobe products, where "cross-platform" means Windows and Mac, so when I say "cross-platform" in this context, I am also referring to that same set of platforms.
If I'm talking about a mobile app and I say "cross-platform" I probably meant iOS and Android. It would be strange to say "what about Linux??" in that context.
So here we are talking about competitors to Adobe products, where "cross-platform" means Windows and Mac, so when I say "cross-platform" in this context, I am also referring to that same set of platforms.