Read history, then comment, okay?
The PARC machine barely scratched the surface of what could be done, and it was far from being packaged in a way that could be marketed to consumers. It was inspiration, and any engineer knows that's a long, long way from a working product.
Even Microsoft has gone its own way with Windows after some heavy overlap with MacOS and other windowing systems (DESQview in partcular). Windows 3.1 was more different, and Windows 95 borrowed more heavily from OS/2, which was wildly different from MacOS. If anything Apple was forced to adopt the right-click menu popularized by Microsoft since it became the de-facto standard.
Meanwhile other companies have damning memos that say "Make it look exactly like Apple's product".
This is pure conjecture, but every company does it. My point was let's not act like Apple is innocent and does not.
Xiaomi has built its entire company on blatant theft of designs. Let's not say "oh, it's okay because Apple once did X" which is like saying murder is no different from a speeding ticket since both things are illegal.
Their ideal product entry point is when consumers are familiar with the product but are unhappy with the current offerings because they lack the right contextual fit.
Maybe if you have a specific example here of where Apple's flagrantly copied something like Xiaomi has we can talk specifics.
Apple Watch: It's a smart watch, they didn't invent the category, but it's a novel form-factor, instantly recognizable. The operating system is also highly distinct from others. You'd never confuse an Apple Watch for anything but an Apple Watch. Some of the Android based ones are going out of their way to look like non-smart watches. At least Motorola has their own design language here.
F.lux: Significant functional overlap but these sorts of tools have been around since the 1990s. It's not like F.lux invented this, they just popularized it. Maybe it was a dick move on Apple's part, or maybe it was just a thing they thought should be core to their product.
When Microsoft wanted to add faxing functionality to Windows they could have bought WinFax, but they instead made their own thing. Is this stealing?
I think your definition of stealing and copying is extremely loose, to the point where the term has lost all meaning.
Your comments use words similar to mine like "the" and "a". Are you stealing my words?
http://web.stanford.edu/dept/SUL/sites/mac/parc.html