Can get a pretty good idea about what both Android & Windows are upto. I know folks who spent time mitm connections from both to get an idea + lots of folks spend a lot of time examining/ reverse engineering both operating systems. Android's more complex as its a family of OSs, but all have lots of open code via AOSP
Security differences are covered well in https://madaidans-insecurities.github.io/security-privacy-advice.html
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