The TSMC Arizona plant is already operational they started production of TSMC 4nm process node this month, and will be ramping up volume over the next few months.
Even so, the ramp-up to full capacity is going to take a while - and even at full capacity it's not going to be a replacement for the facilities in Taiwan.
They don't have to replace all of the Taiwanese manufacturing, just the chips that are US bound. There are plenty of customers in other countries that need TSMC chips.
https://www.reuters.com/technology/tsmc-begins-producing-4-n...