The Mac Pro is an exception, which carries a decent graphics card inside, but it’ll cost you a lot more than a comparable Windows PC would. The discrete graphics cards used in the high-end Macs aren’t all that great, and you don’t have the choice of the more powerful graphics cards you would in some Windows PCs.
However, Macs aren’t exactly designed for gaming. It’s not like a PC has some magic video game component that your Mac lacks.
This means there’s no real hardware barrier to gaming on a Mac. They’re just an Intel x86 computer in a fancier case with a different operating system. Macs are made of the same components as any other PC.