They may have used the same five nanometer process, but that doesn't mean Apple's own costs went down. I don't know what their negotiations look like, but TSMC have stated that they'd be raising prices on already-established chip technology. In general, given supply issues for many of the components that go into making a laptop over the past few years, it would be a miracle for Apple's costs not to have risen.

Combine that with general increases in the price level, and 20% is probably not that far off.

A capitalistic company gonna do capitalistic things - shocking. Shocking!