Food for your thought, basic computer stuff:
It's not the CPU that supports (or doesn't support) thunderbolt. There are thunderbolt controllers that you put inside a computer, they connect to the CPU via PCIe. As long as your computer has PCIe, you can add thunderbolt to it. Apple, ARM, Intel, Qualcomm, AMD, doesn't matter. I didn't feel like I needed to explain this, being on a computer forum and all, but now I know that I do.
Oh Castiel, as usual you don't understand what you're googling. Theoretical support for PCIe 4.0 doesn't have direct benefit to current M1 product lineup because current M1 product lineup at Apple doesn't come with any PCIe slots or expansion possibilities, so you won't be adding any "thunderbolt to it". I didn't think I needed to explain this, to quote your cringe/shadenfreude. It has nothing to do with arm, it's a product architecture issue, not CPU architecture issue. Exhausting. Just... exhausting interlocutor.