在LazyVGrid中给予spacing: 0表示垂直间距，在GridItem中赋予spacing: 0表示水平间距。
这里是一个演示。在Xcode 12 / iOS 14上测试
x1c 0d1x的数据

struct TestImagesInGrid: View {
    @State private var imageNames: [String]

    private let threeColumnGrid = [
        GridItem(.flexible(minimum: 40), spacing: 0),
        GridItem(.flexible(minimum: 40), spacing: 0),
        GridItem(.flexible(minimum: 40), spacing: 0),
    ]

    init() {
        _imageNames = State(initialValue: (0..<8).map { _ in
            "image_\(Int.random(in: 1...3))"
        })
    }

    var body: some View {
        LazyVGrid(columns: threeColumnGrid, alignment: .leading, spacing: 0) {
            ForEach(imageNames.indices) { i in
                Image(imageNames[i]).resizable()
                    .aspectRatio(1, contentMode: .fill)
                    .border(Color.black)
            }
        }
    }
}

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简短的回答：

GridItem(.flexible(), spacing: 0),

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