"To be clear, wafer agreements are signed 2-3 years before the chip makes it into HVM and TSMC can build fabs faster than that so there will be no N3 shortages for anyone who signed a wafer agreement (apple, AMD, NVIDIA, QCOM, etc…). If they need more chips than what they signed up for, which happens, there may be shortages. This is how TSMC and the foundry business works. It’s all about the wafer agreements."
That is not how capacity planning works. You dont built it and hope for them to come.
If others were willing to paid, take the risk and book in advance they will have the capacity the need. But rarely anyone was will to pay the price premium. They wait for it to become a little more mainstream.
What is the point of having the best tech in 2021 if all capacity is allocated to a single customer?