It is lot harder technically and politically for apple to replace TSMC part of the value chain. Apple will loose a lot of brand value if it directly employees cheap Asian labour.

They could in theory move the production to U.S. however without the ecosystem of talent, suppliers and partners that Taiwan or china has it will be hard .

They already spent 10+ years improving their iPad chips, switching made sense especially given intel lack of reasonable roadmap, the effort to integrate TSMC part of the chain does not have the same value given the risks today.

TSMC is a foundry, there are very few companies worldwide with capacity to do the fab work that TSMC does and Apple is definitely not one of those.

Are you confusing with Foxconn or other parts assemblies that Apple use? Because for Apple to roll out their own fab infrastructure would be a massive undertaking with very little benefit.

There are a lot of inefficiencies in the companies that fab chips. (If you ever need an example of how consolidation / lack of competition leads to less than optimal output, semiconductor fabrication is it.) Stuff that takes on the order of hours or days that should instead take take a minute or two, tops. Information that should be take seconds to access and available at any time is instead put together manually. So much of what would appear to be institutional knowledge at these places is little more that cargo cult voodoo that may or may not have any significant impact on the product. Dumb mistakes (and the subsequent efforts to cover them up) by a workforce whose primary motivations are centered around making it through the day without getting in trouble and without giving away how little they understand and appearing as stupid as they feel.

Honestly, if Apple or Google or any other company with top-tier engineering wanted to get into the game and were serious about it, they could be competitive in a < 10-year time frame, and easily making laps around the competition past that.

This seemed obvious to me at first, but less the more I think of it. Samsung, for instance. Apple is already using 100% of 5nm capacity, so they are basically leasing an entire fab. The technology curve for fabs will bend in the direction of lower capital investment, smaller batches, and shorter turnaround, not smaller dimensions.

Are you thinking of Foxconn? I don't think anything you said makes sense for TSMC.

Will these chips - or similar ones - be available to buy for others than apple, too?