Don't hesitate to use .aspectRatio instead of GeometryReader in calculations based on relative container size. Especially when your subview has a dynamic content size effecting parent size back. Here's an example comparing two these approaches making a bar chart

GeometryReader vs AspectRatio

struct GeometryReaderApproach: View {
    private let values: [Double] = [152, 355, 475, 78, 173, 295]
    private let maxValue: Double
    
    init() { maxValue = values.max() ?? 0 }
    
    var body: some View {
        VStack {
            let data = Array(zip(values.indices, values))
            // Why not use .enumerated? Well, in general it's is not necessarily the index of the paired value.
            ForEach(data, id: \.0) { (index, value) in
                HStack {
                    Text("\(index): ")
                    
                    GeometryReader { geometry in
                        ZStack(alignment: .leading) {
                            RoundedRectangle(cornerRadius: 6)
                                .fill(Color.gray)
                            
                            RoundedRectangle(cornerRadius: 6)
                                .fill(Color.green)
                                .frame(width: value / maxValue * geometry.size.width)
                        }
                    }
                    .frame(height: 15)
                }
            }
        }
        .padding()
    }
}

struct AspectRatioApproach: View {
    private let values: [Double] = [152, 355, 475, 78, 173, 295]
    private let maxValue: Double
    
    init() { maxValue = values.max() ?? 0 }
    
    var body: some View {
        VStack {
            let data = Array(zip(values.indices, values))
            ForEach(data, id: \.0) { (index, value) in
                HStack {
                    let baseRatio: Double = 20 / 1
                    Text("\(index): ")
                    
                    ZStack(alignment: .leading) {
                        RoundedRectangle(cornerRadius: 6)
                            .fill(Color.gray)
                            .aspectRatio(baseRatio, contentMode: .fit)
                            .frame(maxWidth: .infinity)
                        
                        RoundedRectangle(cornerRadius: 6)
                            .fill(Color.red)
                            .aspectRatio(value / maxValue * baseRatio, contentMode: .fit)
                            .aspectRatio(baseRatio, contentMode: .fit)
                    }
                    .fixedSize(horizontal: false, vertical: true)
                    // Fix size to prevent bar from resizing
                }
            }
            
            Text("Hello")
        }
        .padding()
    }
}