Possible solution is to use dynamic width for labels applied by max calculated one using view preferences.

Here is a demo. Tested with Xcode 13beta / iOS15

Note: the ViewWidthKey is taken from my other answer https://stackoverflow.com/a/63253241/12299030

struct ContentView: View {
    @State private var colorName: Colors = .red
    @State private var maxWidth = CGFloat.zero

    var body: some View {
        Picker("Select color", selection: $colorName) {
            ForEach(Colors.allCases) { color in
                HStack {
                    color.asColor.aspectRatio(contentMode: .fit)
                    Text(color.rawValue)
                }
                .background(GeometryReader {
                    Color.clear.preference(key: ViewWidthKey.self, 
                        value: $0.frame(in: .local).size.width)
                })
                .onPreferenceChange(ViewWidthKey.self) {
                    self.maxWidth = max($0, maxWidth)
                }
                .frame(minWidth: maxWidth, alignment: .leading)
            }
        }
    }
}

backup

Possible solution is to use dynamic width for labels applied by max calculated one using view preferences.

Here is a demo. Tested with Xcode 13beta / iOS15

Note: the ViewWidthKey is taken from my other answer https://stackoverflow.com/a/63253241/12299030

struct ContentView: View {
    @State private var colorName: Colors = .red
    @State private var maxWidth = CGFloat.zero

    var body: some View {
        Picker("Select color", selection: $colorName) {
            ForEach(Colors.allCases) { color in
                HStack {
                    color.asColor.aspectRatio(contentMode: .fit)
                    Text(color.rawValue)
                }
                .background(GeometryReader {
                    Color.clear.preference(key: ViewWidthKey.self, 
                        value: $0.frame(in: .local).size.width)
                })
                .onPreferenceChange(ViewWidthKey.self) {
                    self.maxWidth = max($0, maxWidth)
                }
                .frame(minWidth: maxWidth, alignment: .leading)
            }
        }
    }
}

Possible solution is to use dynamic width for labels applied by max calculated one using view preferences.

Here is a demo. Tested with Xcode 13beta / iOS15

Note: the ViewWidthKey is taken from my other answer https://stackoverflow.com/a/63253241/12299030

struct ContentView: View {
    @State private var colorName: Colors = .red
    @State private var maxWidth = CGFloat.zero

    var body: some View {
        Picker("Select color", selection: $colorName) {
            ForEach(Colors.allCases) { color in
                HStack {
                    color.asColor.aspectRatio(contentMode: .fit)
                    Text(color.rawValue)
                }
                .background(GeometryReader {
                    Color.clear.preference(key: ViewWidthKey.self, 
                        value: $0.frame(in: .local).size.width)
                })
                .onPreferenceChange(ViewWidthKey.self) {
                    self.maxWidth = max($0, maxWidth)
                }
                .frame(minWidth: maxWidth, alignment: .leading)
            }
        }
    }
}

Possible solution is to use dynamic width for labels applied by max calculated one using view preferences.

Here is a demo. Tested with Xcode 13beta / iOS15

Note: the ViewWidthKey is taken from my other answer https://stackoverflow.com/a/63253241/12299030

struct ContentView: View {
    @State private var colorName: Colors = .red
    @State private var maxWidth = CGFloat.zero

    var body: some View {
        Picker("Select color", selection: $colorName) {
            ForEach(Colors.allCases) { color in
                HStack {
                    color.asColor.aspectRatio(contentMode: .fit)
                    Text(color.rawValue)
                }
                .background(GeometryReader {
                    Color.clear.preference(key: ViewWidthKey.self, 
                        value: $0.frame(in: .local).size.width)
                })
                .onPreferenceChange(ViewWidthKey.self) {
                    self.maxWidth = max($0, maxWidth)
                }
                .frame(minWidth: maxWidth, alignment: .leading)
            }
        }
    }
}

backup