Apple didn't do shit except maybe increase the TSMC bottom line.
TSMC continuously made the best most reliable independent process at scale since the iPhone came out, and Apple paid to get the combination of reliability and performance.
In about 2016 TSMC surpassed even Intel because Intel stumbled on their 10nm process. But at the time TSMC passed Intel, Apple was only about 10-15% of TSMC revenue.
At the same Time AMD became a major customer, and Nvidia has also mainly used TSMC apart from a short period where they used Samsung.
The success of TSMC is because of TSMC skill and business tenacity, not because of Apple or any other customer.
Apple basically had 3 places to go, after they asked Intel and Intel said no.
Global foundries, a company already struggling, and tied to supply AMD.
Samsung A company with wearying quality and output in the highest end of their capability.
TSMC A company with years of showing high stability at volume, and the leader on performance for independent production, and with high trustworthiness.
The idea of Apple making their own foundry at the time would have been insane. They simply chose the best as most other high performance high volume chip customers did.
Now TSMC is the undisputed leader, with Samsung and Intel playing catch-up as TSMC now leads in performance, yield and volume production.
Yes smartphones helped TSMC achieve the revenue required, but it wasn't Apple as a customer that made TSMC into what they are today, TSMC was getting there even before Apple became a major customer.
What really helped TSMC though, was that Intel initially discarded the idea of making the chip for Apple, because Intel saw it as a low profit margin market, which they had no interest in.
So TSMC was helped by the arrogance of the only chip manufacturer that was better than TSMC.