This is about FABs and not chip designs. Imagine a parallel universe where Apple was sourcing AMD chips (they actually did for graphic cards) and then went to TSMC to whom AMD is also a customer.

Intel is both at the same time, AMD and TSMC.

Note that I said M6 and beyond. I know the chip designs being produced will remain Apple's.

Other commenters in the thread talk about how Intel's node is simply inferior to TSMC's and will bottleneck the performance of the same chip designs simply by being bad. I hope that is not the case and/or that I won't have to settle for an Intel node inside my Apple chips. (They better not try to pull an AMD where some chips simply have utterly kneecapped performance for no good reason.)