After being available on Linux for a couple of months now, Total War: Warhammer has finally made its way to Mac as well. As with pretty much every game on Steam, if you own Total War: Warhammer you will have free access to both the Linux and Mac versions alongside the PC one. In other words, you don't have to buy an extra copy for each platform!
Much like the Linux version, the Mac port of Total War: Warhammer has not been made by Creative Assembly themselves, but rather by Feral Interactive. You might know them from the Mac and Linux ports of XCOM 2, Tomb Raider, Deus Ex: Mankind Divided, Hitman, Mad Max, and the list goes on. Their ports have pretty much always been rock solid, and while I haven't tested the Mac version myself I have no doubts that its going to be perfectly playable, especially when you consider how long they took to actually create it.
If you're new to Total War: Warhammer and you aren't even sure if this is the type of game you might enjoy, you can find my detailed review by heading over here. Long story short, "Total War: Warhammer is a crossover between two franchises I've enjoyed for many years now, and I'm delighted to say that it manages to be faithful to both sides, but most importantly, an actually enjoyable experience on its own!"
On the other hand, if you prefer a more basic overview of the gameplay and strategies you'll get to employ, here's the official "What is Total War: Warhammer" video. Enjoy!