.NET 9 - Raise Min iOS supported version to 13.0 or 15.0

[Redth]

There have been a number of new API’s made available on later versions of iOS that will help MAUI’s implementation become simpler and more reliable, while decreasing the maintenance cost of supporting older, minimally used platform versions.

Some examples:

• UICollectionView + Compositional Layouts (13+)
• UIButtonConfiguration (iOS15+)

Consider the version information on iOS version by device — iOS Ref our current (.NET 8) and future (.NET 9) oldest supported devices can be summarized below (year in parenthesis is :

	.NET 8	.NET 9
iPhone	iPhone 5 (2012)	iPhone 6S/6S Plus (2015)
iPad	iPad gen4 (2012)	iPad Air 2 (2014) / iPad mini 4 (2015)
iPod	iPod touch gen6 (2015)	iPod touch gen7 (2019)

(YEAR) is the date when the device was first released

iOS 13 vs 15

We are also considering skipping directly to iOS 15 as any device which supported iOS 13, Apple also continued to support updating to iOS 15.

It’s also worth considering Apple’s self reported statistics on iOS version usage: App Store - Support - Apple Developer.
Based on these statistics, 89% of all devices are using iOS 16 or newer. Apple does not specify the iOS versions for the remaining 11%, however it’s reasonable to expect some amount of those are on 13, 14, or 15.

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I believe that we just need to update the:

<PropertyGroup Condition="'$(_MauiTargetPlatformIsiOS)' == 'True'">
    <SupportedOSPlatformVersion>11.0</SupportedOSPlatformVersion>
    <TargetPlatformMinVersion>11.0</TargetPlatformMinVersion>

in our Directory.Build.targets. This will mark our assemblies as needing new OS versions via a slew of warnings in the user projects. Users will need to manually update their csproj.

We could have a look at moving the SupportedOSPlatformVersion items into the maui targets and the user can override in the IDE and/or in the csproj. This way the csproj is shorter and we can bump it when we need to.

Todo:

• Raise the version in MAUI repo targets - Increase MAUI library supported version to 13.0 #22794
• Look at adding a descriptive error/warning when we detect a maui project with explicitly older version set (the default SDK error might not be super helpful so we should add something better ourselves to help with upgrading projects) - Implicitly set SupportedOSPlatformVersion #23857
• Add implicit defaults to MAUI's .targets so that these can be removed from project templates - Implicitly set SupportedOSPlatformVersion #23857
• Ensure documentation is up to date describing these properties
• Remove the properties from the template - Implicitly set SupportedOSPlatformVersion #23857
• Validate project property pages work correctly with all the changes