First, where are you located? Model years work differently in different places. Either way - 2021 or 2022, the car is the same.
Second, yes, the AMD MCU will likely make it to the Model 3 - eventually. Right now, it's just rumors. There's ONE example going around the internet of the AMD MCU in a Model Y out of China - none that I've seen in a Model 3 yet. So, it could be a couple of months, or it could be a year or more before the MCU is updated in the Model 3, and even then, there's a good possibility that Tesla will offer a retrofit.
Just think of the fun you could be having in your M3P while you're waiting that completely unknown amount of time!