Sliding sidebar (hover to show) in SwiftUI. See more or less how I built it: https://youtu.be/FYrNgz2xADc

Sidebar.swift

import SwiftUI

struct Sidebar<Content: View>: View {
    @State var visible: Bool = false
    var content: () -> Content
  
    init(@ViewBuilder content: @escaping () -> Content) {
        self.content = content
    }

    var body: some View {
        ZStack(alignment: .leading) {
            HStack(spacing: 0) {
                Spacer()
                    .frame(width: 16)
                RoundedRectangle(cornerRadius: 8)
                    .fill(.black.opacity(!visible ? 0.2 : 0))
                    .offset(x: !visible ? 0 : -20)
                    .frame(width: 4, height: 40)
                Spacer()
            }
            .frame(maxWidth: 80, maxHeight: 500)

            ZStack {
                content()
                    .frame(width: 200)
            }
            .frame(maxWidth: visible ? 200 : 100, maxHeight: visible ? 500 : 600)
            .background(
                RoundedRectangle(cornerRadius: 16).fill(Color.white)
                    .shadow(color: .black.opacity(0.1), radius: 12, x: 0, y: 1)
                    .shadow(color: .black.opacity(0.2), radius: 1)
            )
            .offset(x: visible ? 20 : -100)
            .opacity(visible ? 1 : 0)
        }
        .frame(maxHeight: .infinity)
        .onHover { next in
            withAnimation(.interactiveSpring(duration: 0.2)) {
                visible = next
            }
        }
    }
}