SwiftUI overlay/background backport issue

Using Swift
,
1

Hello, I wonder why new overlay (and background too) functions with @ViewBuilder introduced in iOS 15 isn't available in previous versions, but Section inits are available? Probably according to articles here and here in the internet it uses _alwaysEmitIntoClient swift attribute. Is it SwiftUI API design flaw? Is it possible to backport or not due another generic V instead of Overlay

iOS 15 overlay, which is limited only to iOS15:

@inlinable public func overlay<V>(alignment: Alignment = .center, @ViewBuilder content: () -> V) -> some View where V : View

pre iOS 15 overlay:

    @available(iOS, introduced: 13.0, deprecated: 100000.0, message: "Use `overlay(alignment:content:)` instead.")

    @available(macOS, introduced: 10.15, deprecated: 100000.0, message: "Use `overlay(alignment:content:)` instead.")

    @available(tvOS, introduced: 13.0, deprecated: 100000.0, message: "Use `overlay(alignment:content:)` instead.")

    @available(watchOS, introduced: 6.0, deprecated: 100000.0, message: "Use `overlay(alignment:content:)` instead.")

    @inlinable public func overlay<Overlay>(_ overlay: Overlay, alignment: Alignment = .center) -> some View where Overlay : View

Section iOS 15 ViewBuilder init, which is available in previous versions:

 public init(@ViewBuilder content: () -> Content, @ViewBuilder header: () -> Parent, @ViewBuilder footer: () -> Footer)

pre iOS 15 init

extension Section where Parent : View, Content : View, Footer : View {
    @available(iOS, deprecated: 100000.0, renamed: "Section(content:header:footer:)")

    @available(macOS, deprecated: 100000.0, renamed: "Section(content:header:footer:)")

    @available(tvOS, deprecated: 100000.0, renamed: "Section(content:header:footer:)")

    @available(watchOS, deprecated: 100000.0, renamed: "Section(content:header:footer:)")

    public init(header: Parent, footer: Footer, @ViewBuilder content: () -> Content)

}