My theory is that they will switch low power devices like Macbook Airs to ARM chips while keeping high power devices on Intel for now. They will sell millions of those low power devices, but designing a competitive workstation chip takes a lot of money and they won't sell enough Mac Pros to offset that cost. Intel makes those CPUs for servers and basically rebrands them for workstations. Apple is not in the server business.

May be they'll just discontinue powerful Pro devices at some point and that's about it.

May be they'll manage to create powerful CPUs using chiplet design, but I absolutely have no idea whether it's cheap or not.