ios-analysis | Automated Binary Analysis on iOS | Reverse Engineering library

You have misread the statement in your first point. Microsoft doesn't say that using 32-bit is bad, so you need to use 64-bit. Just the opposite.

Basically, it is always preferable to use 64-bit float operations. They are enabled by default and according to the Floating Point Operations in Xamarin.iOS docs:

While this higher precision is closer to what developers expect from floating point operations in C# on the desktop, on mobile, the performance impact can be significant.

Let's see what the Code Analysis tool is:

Xamarin.iOS analysis is a set of rules that check your project settings to help you determine if better/more optimized settings are available.

So, even though it is preferable to use 64-bit floats, this isn't always the best choice. When you run the Code analysis tool, it will scan your project to see if there is a better suited configuration for your solution (it depends on the project's flow).

Occasionally, the 64-bit floats may do you more harm than gain. In this case, the linter will warn you with XIA0005: Float32Rule, which will suggest that you uncheck the option, like the Microsoft's message says.