Appleの言う（iOSの）boldはsemibold

• 1行目: 明示的にboldを指定した
• 2行目: 暗黙的にboldを指定した(boldSystemFont(ofSize:)*1, bold()*2 )
• 3行目: 明示的にsemiboldを指定した

環境

• macOS: Sonoma 14.6.1 (23G93)
• Xcode: 15.4(15F31d)
• Swfit: 5.10

コード

import SwiftUI

struct ContentView: View {
    var body: some View {
        HStack {
            VStack(alignment: .leading, spacing: 4) {
                Text("UIKit")
                VStack(alignment: .leading, spacing: 0) {
                    Label(font: .systemFont(ofSize: 20, weight: .bold))
                        .fixedSize()
                    Label(font: .boldSystemFont(ofSize: 20))
                        .fixedSize()
                    Label(font: .systemFont(ofSize: 20, weight: .semibold))
                        .fixedSize()
                }
            }
            VStack(alignment: .leading, spacing: 4) {
                Text("SwiftUI")
                VStack(alignment: .leading, spacing: 0) {
                    Text("Lorem ipsum")
                        .font(.system(size: 20, weight: .bold))
                    Text("Lorem ipsum")
                        .font(.system(size: 20))
                        .bold()
                    Text("Lorem ipsum")
                        .font(.system(size: 20, weight: .semibold))
                }
            }
        }
    }
}

struct Label: UIViewRepresentable {
    let font: UIFont

    func makeUIView(context: Context) -> UILabel {
        let label = UILabel()
        label.text = "Lorem ipsum"
        label.font = font

        return label
    }

    func updateUIView(_ uiView: UILabel, context: Context) {}
}

*1:https://developer.apple.com/documentation/uikit/uifont/1619039-boldsystemfont

*2:https://developer.apple.com/documentation/swiftui/font/bold()