RoundedRectangle shape and .cornerRadius modifier is used to round specific corners:

Use such way:

RoundedRectangle(topLeft: 0, 
                topRight: 16, 
                bottomLeft: 16,
                bottomRight: 16)

If you have radiuses on one side that larger than half of height or half of width:

then use chain of modifiers:

Text("Corner radius modifier")
                .foregroundColor(.black)
                .padding(16)
                .background (
                    Color.purple
                        .cornerRadius(200, corners: .topLeft)
                        .cornerRadius(200, corners: .bottomLeft)
                )

Bubble shape and .bubble modifier is used to draw messages or tips:

Use such way:

VStack {
    Text("Hi!")
        .padding(.horizontal, 12)
        .padding(.vertical, 8)
        .background(
            Bubble.init(type: .send,
                        cornerRadius: 20,
                        tail: (width: 6, height: 15))
            .stroke(.gray, lineWidth: 2)
        )
        .frame(maxWidth: .infinity,
               alignment: .trailing)

    Text("Wassup!")
        .padding(.horizontal, 12)
        .padding(.vertical, 8)

        .background(
            Bubble.init(type: .received,
                        cornerRadius: 20,
                        tail: (width: 6, height: 15))
            .stroke(.gray, lineWidth: 2)
        )
        .frame(maxWidth: .infinity,
               alignment: .leading)
}
.padding(20)

or via modifier:

VStack(spacing: 20) {
    Text("Custom bubble ✌🏻 \nLeading")
        .foregroundColor(.white)
        .padding(16)
        .bubble(.received,
                withStroke: .clear,
                lineWidth: 2,
                fill: .black.opacity(0.7))
        .frame(maxWidth: .infinity, alignment: .leading)
        
    Text("Custom bubble ✌🏻\nTrailing")
        .foregroundColor(.white)
        .padding(16)
        .bubble(.send,
                withStroke: .clear,
                lineWidth: 2,
                fill: LinearGradient(
                    gradient: Gradient(colors: [.blue.opacity(0.9), .blue.opacity(0.6)]),
                    startPoint: .leading,
                    endPoint: .trailing
                ))
        .frame(maxWidth: .infinity, alignment: .trailing)
}

Wave shape and .waved modifier is used to draw animated wave:

• upside-waved variant:

• inside-waved variant:

• no wave, classical variant:

Use such way:

HStack {
    ...
    /* Buttons */
    ...
}
.background(
    Color.black.opacity(0.8)
        .waved(corner: cornerRadius,
               height: waveHeight,
               startX: waveX,
               length: waveLength)
)

Diamond shape and .diamond modifier is used to draw rhombuses or quadrangles:

Use such way:

Text("Diamond")
    .padding(.horizontal, 24)
    .padding(.vertical, 16)
    .background(
        Diamond()
            .stroke(.blue, lineWidth: 2)
    )

or via modifier:

Text("Diamond modifier")
    .foregroundColor(.black)
    .padding(24)
    .diamond(top: .init(x: 40, y: 0),
             bottom: .init(x: 0, y: 0),
             withStroke: .black,
             lineWidth: 2.0,
             fill: .yellow)