Based on the 100 Days projects I started on a custom project, but in the class definitions below the RegattaList does not conform to RandomAccessCollection so I cannot use it in a ForEach. I cannot see what the issue is as it is an array of Regatta which has a UUID?

import Foundation
import SwiftUI

class Regatta: Identifiable, Codable {
    var id : UUID = UUID()
    var name = "Sample Regatta"
    var scoreType: ScoreMethod = .Lowpoint
    var startDate: Date = Date()
    var endDate: Date = Date()
    var contact = "Me"
    var boatClass: BoatClass = .DF95
    var skippers: [Skipper]
    //var scores :
}

@MainActor class RegattaList: ObservableObject, RandomAccessCollection {

    @Published  var regattas: [Regatta]

    let savePath = FileManager.documentsDirectory.appendingPathComponent("SavedRegattas")

    init() {
        do {
            let data = try Data(contentsOf: savePath)
            regattas = try JSONDecoder().decode([Regatta].self, from: data)
        } catch {
            regattas = []
            // why doesnt this work?
            //regattas = [Regatta(name: "Getting Started", scoreType: ScoreMethod.Lowpoint, startDate: Date(), endDate: Date(), contact: "You!")]
        }
    }
    private func save() {
        do {
            let data = try JSONEncoder().encode(regattas)
            try data.write(to: savePath, options: [.atomic, .completeFileProtection])
        } catch {
            print("Unable to save data.")
        }

    }
    func add(_ regatta: Regatta) {
        regattas.append(regatta)
        save()
    }

    let dateFormatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateStyle = .short
        //formatter.timeStyle = .medium
        return formatter
    }()
}

class Skipper: Codable {
    var id: UUID
    var firstName: String
    var lastName: String
    var boatNum: Int
    var sailNum: Int
    static func ==(lhs: Skipper, rhs: Skipper) -> Bool {
        return lhs.lastName == rhs.lastName && lhs.sailNum == rhs.sailNum
    }
}

Codable will only work if ALL the elements are codable. In the Regatta class you have, Skipper,ScoreMethod and BoatClass. You have given the Skipper class and see that it is Codable, however the other two (which is assume are enums) these also need to confrom to Codable

If you remove them you will see that the code should work!

struct Regatta: Identifiable, Codable {
    var id = UUID()
    var name: String
//    var scoreType: ScoreMethod = .Lowpoint
    var startDate: Date
    var endDate: Date
    var contact: String
//    var boatClass: BoatClass = .DF95
    var skippers: [Skipper]
}

class RegattaList: ObservableObject {

    @Published  var regattas: [Regatta]

    let savePath = FileManager.documentsDirectory.appendingPathExtension("SavedRegattas")

    init() {
        do {
            let data = try Data(contentsOf: savePath)
            regattas = try JSONDecoder().decode([Regatta].self, from: data)
        } catch {
            regattas = []
            // why doesnt this work?
            //regattas = [Regatta(name: "Getting Started", scoreType: ScoreMethod.Lowpoint, startDate: Date(), endDate: Date(), contact: "You!")]
        }
    }

    private func save() {
        do {
            let data = try JSONEncoder().encode(regattas)
            try data.write(to: savePath, options: [.atomic, .completeFileProtection])
        } catch {
            print("Unable to save data.")
        }

    }

    func add(_ regatta: Regatta) {
        regattas.append(regatta)
        save()
    }

    let dateFormatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateStyle = .short
        //formatter.timeStyle = .medium
        return formatter
    }()

}

struct Skipper: Codable {
    var id: UUID
    var firstName: String
    var lastName: String
    var boatNum: Int
    var sailNum: Int

    static func ==(lhs: Skipper, rhs: Skipper) -> Bool {
        return lhs.lastName == rhs.lastName && lhs.sailNum == rhs.sailNum
    }
}

extension FileManager {
    static var documentsDirectory: URL {
        let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
        return paths[0]
    }
}

struct ContentView: View {
    @StateObject private var regattaList = RegattaList()

    var body: some View {
        List {
            ForEach(regattaList.regattas) { regatta in
                Text(regatta.name)
            }
        }
    }
}

Thanks for the input Guys. After correcting the ForEach I found the issue to be that Regatta was not hashable but could fix that with a hash func definition. Good learning experience

Not sure why you would need to conform Regatta to Hashable. Identifiable should be sufficient for the ForEach to work, unless something else is going on in the code you haven't shown us.