Simple custom SwiftUI tabbar based on https://www.youtube.com/watch?v=6W2vuwWTAU4&list=PLimqJDzPI-H9h7HS40v-5QdwxoC4jrXQu&index=1

CustomTabBarExample.Swift

//
//  CustomTabBarExample.swift
//
//  Created by Matt Pfeiffer on 10/22/23.
//

import SwiftUI

struct CustomTabBarExample: View {
    @State var index: Int = 0
    
    var body: some View {
        ZStack {
            Color.red.hueRotation(Angle(degrees: Double(90 * index+1)))
            CustomTabBar(index: $index)
        }
    }
}

#Preview {
    CustomTabBarExample()
}

struct CustomTabBar: View {
    @Binding var index: Int
    
    var body: some View {
        VStack {
            Spacer()
            CustomTabs(index: $index)
        }
    }
}

struct CustomTabs: View {
    @Binding var index: Int
    
    let images: [Image] = [Image(systemName: "pencil.circle"), 
                           Image(systemName: "eraser"),
                           Image(systemName: "scribble"),
                           Image(systemName: "pencil.tip")]
    
    var body: some View {
        HStack {
            ForEach(0...3, id: \.self) { index in
                Button(action: {
                    self.index = index
                }, label: {
                    images[index]
                        .resizable()
                        .frame(width: 24, height: 24)
                })
                .foregroundColor(Color.black.opacity(self.index == index ? 1 : 0.2))
                .frame(maxWidth: .infinity)
                
                // middle button
                if index == 1 {
                    Button(action: {
                        
                    }, label: {
                        Image(systemName: "plus.circle.fill").renderingMode(.original)
                            .resizable()
                            .frame(width: 48, height: 48)
                    })
                    .offset(y: -25)
                    .frame(maxWidth: .infinity)
                }
            }
        }
        .padding(.top, 35)
        .background(Color.white)
        .clipShape(CShape())
    }
}

struct CShape: Shape {
    func path(in rect: CGRect) -> Path {
        return Path { path in
            path.move(to: CGPoint(x: 0, y: 35))
            path.addLine(to: CGPoint(x: 0, y: rect.height))
            path.addLine(to: CGPoint(x: rect.width, y: rect.height))
            path.addLine(to: CGPoint(x: rect.width, y: 35))
            
            path.addArc(center: CGPoint(x: rect.width / 2, y: 35),
                        radius: 35,
                        startAngle: .zero,
                        endAngle: .init(degrees: 180),
                        clockwise: true)
        }
    }
}