Use the new `containerBackground` modifier for widgets if iOS 17 is available, or easily fallback to a `ZStack` with standard padding.

WidgetBackground.swift

//
//  WidgetBackground.swift
//
//  Created by Kyle Bashour on 6/5/23.
//

import SwiftUI

struct WidgetBackground<Background: View>: ViewModifier {
    private let background: Background

    init(@ViewBuilder background: () -> Background) {
        self.background = background()
    }

    func body(content: Content) -> some View {
        if #available(iOS 17, watchOS 10, *) {
            content.containerBackground(for: .widget) {
                background
            }
        } else {
            ZStack(alignment: .leading) {
                background
                content.padding()
            }
        }
    }
}

extension View {
    func widgetBackground(@ViewBuilder background: () -> some View) -> some View {
        modifier(WidgetBackground(background: background))
    }
}