Welcome to the forum.
Adobe allows for a user to have PrE installed on two personal computers, just not running at the same time. However, I do not know about having one on a Mac, and a PC. Maybe Steve, who runs PrE on both a Mac and a PC, can give you a definitive answer to that.
Yes, you can have it on two different computers -- even if one is a Mac and the other is a PC.
Great to know. I assumed that it would be that way, as the installation media are X-platform, with both versions in the pack.
In other Adobe programs, where there are not X-platform versions, one needs to cross-grade, platform to platform. Glad to hear that PrE allows for both platforms.