For the most part, the platform doesn’t matter.
You’ll get better performance from a PC if everything works, but your best bet for stability is probably going to be the iOS or iPad app because Zwift can actually test releases on a reasonable number of device + OS combinations, whereas for PCs it’s practically impossible. It’s not unheard of that something just doesn’t work on a particular combination of PC parts, and debugging it is a pain.
On the other hand, you lose ANT+ connectivity, and Bluetooth can be fussy at times.
Pretty much any PC will work fine inasmuch as it does. 4K adds basically nothing on the game side, you could just as well run it at 1080p and upscale it on the TV or possibly your vidcard. Or use 4K if your machine is up for it.
ANT+ dongle with a USB cable (no longer than 3 m/9 ft) so that you can place the dongle right next to your power source.
Use a discrete graphics card, not integrated.
Other than that, it’s up to whatever else you might want to do with the PC. If it’s just Zwift and maybe a media server/player, a small form factor is probably preferable to anything else. If it’s your gaming PC, then just plug the dongle in. Intel + Nvidia is maybe a touch safer bet than AMD but it doesn’t really matter much if you get a recent model.
Alternatively, you could get a M1 Mac to run off of.