What are differences between iOS and Android that might affect how we write for the users of each platform?
The obvious one would be that Apple favors minimalism, as they always have. Android of course also wants minimalism where possible, but they are more willing to sacrifice minimalism in favor of flexibility.
These aren't official stances that are really documented anywhere however, and more observations. To note even a few major differences would make for a pretty big answer. It might be easier if you scrolled over their guidelines yourself:
Apple's official UX guidelines: https://developer.apple.com/design/human-interface-guidelines
Androids official UX guidelines: https://developer.android.com/design