I don't think its Apple's fault. Smartphones across the industry are in their 'laptop' phase now where the form has been iterated on and now the only changes to expect are minor tweaks.

Foldables are fun and interesting but they only really solve the problem of 'I wish my iPhone was also an iPad' that maybe 0.001% of customers are bothered about.

Innovation was always going to plateau at some point based on material limitations. How much, for example did TV sets really change between 1960 and 2003? Or stereo equipment? Even games consoles have only really added more buttons and cut some wires* We are lucky enough to have lived through a period of 25 years of intense consumer electronic development but it couldn't continue forever.

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*Obviously the chips and graphics have improved but software hasn't changed much. Halo and Space Invaders are not too dissimilar in gameplay, what with the player effectively strafing and taking cover whilst fighting aliens. And Breath of the Wild is really just NES Zelda with an extra axis.