I’d say the key mistake they made was accepting carrier and OEM intermediation. Apple figured out how to get the carriers out of the way (trading off support down to a single carrier!) while also owning the hardware, and Android OEMs piggybacked on this model.

Microsoft recognized that GUIs were important enough to their future to make what were arguably the best mice available. If they had “caught” mobile, they would have done the same for phones.