Here's my ContentView. If try to changed the number of people, that view doesn't scroll. Thoughts?

struct ContentView: View { let minNumberOfPeople = 2 let maxNumberOfPeople = 20

var dollarFormat : FloatingPointFormatStyle<Double>.Currency {
    let myCurrency = Locale.current.currencyCode ?? "USD"
    return FloatingPointFormatStyle<Double>.Currency( code: myCurrency )
}

@State private var checkAmount = 0.0
@State private var numberOfPeopleIndex = 2
@State private var tipPercentage = 20
@FocusState private var amountIsFocused: Bool

let tipPercentages = [0, 10, 15, 18, 20, 25]

var totalPeople: Int {
    minNumberOfPeople + numberOfPeopleIndex
}

var totalPerPerson: Double {
    checkAmount * (1.0 + Double(tipPercentage)/100.0) / Double(totalPeople)
}
var body: some View {
    NavigationView {
        Form {
            Section(header: Text("How much tip do you want to leave?")) {
                TextField("", value: $checkAmount, format: dollarFormat)
                    .keyboardType(.decimalPad)
                    .focused($amountIsFocused)
            }

            Section(header: Text("How much tip do you want to leave?")) {
                Picker("", selection: $tipPercentage) {
                    ForEach(tipPercentages, id: \.self) {
                        Text($0, format: .percent)
                    }
                }.pickerStyle(.segmented)
            }

            Section(header: Text("Number of People?")) {
                Picker("", selection: $numberOfPeopleIndex) {
                    ForEach(minNumberOfPeople ..< maxNumberOfPeople) {
                        Text("\($0) people")
                    }
                }
            }

            Section(header: Text("Each person contributes")) {
                Text(totalPerPerson, format: dollarFormat)
                    .foregroundColor(Color.red)
            }
        }
            .navigationTitle("WeSplit")
            .toolbar {
                ToolbarItemGroup(placement: .keyboard) {
                    HStack {
                        Spacer()
                        Button("Done With Keyboard") {
                            amountIsFocused = false
                        }
                    }
                }
            }
    }
}

}

I copied and pasted your code over my WeSplit App and it seemed to work fine. Which part isn't scrolling?

You do have the same section header twice:

Section(**header: Text("How much tip do you want to leave?"**)) {
                TextField("", value: $checkAmount, format: dollarFormat)
                    .keyboardType(.decimalPad)
                    .focused($amountIsFocused)
            }

Section(**header: Text("How much tip do you want to leave?"**)) {
                Picker("", selection: $tipPercentage) {
                    ForEach(tipPercentages, id: \.self) {
                        Text($0, format: .percent)
                    }
                }.pickerStyle(.segmented)
            }

I have also tried your code and the Number of People section scroll fine.

Will say a couple of pointer about the code.

var dollarFormat is not just a dollar format it a local currency format so a better name might be something like

var localCurrency : FloatingPointFormatStyle<Double>.Currency {
    let myCurrency = Locale.current.currencyCode ?? "USD"
    return FloatingPointFormatStyle<Double>.Currency( code: myCurrency )
}

Section(header: Text("Each person contributes")) will be depreciated so should use

Section("Each person contributes") {
    Text(totalPerPerson, format: localCurrency)
        .foregroundColor(Color.red)
}

or for more complex headers and footers

Section {
    Text(totalPerPerson, format: localCurrency)
        .foregroundColor(Color.red)
} header: {
    Text("Each person contributes")
} footer: {
    Text("\(tipPercentage == 0 ? "Excluding" : "Including") tip")
}