unarchiveTopLevelObjectWithData is depricated since iOS 15.2 https://developer.apple.com/documentation/foundation/nskeyedunarchiver/2919664-unarchivetoplevelobjectwithdata

instead I tried using unarchivedArrayOfObjects(ofClasses: [Person.self], from: savedPeople) to fix warning:

if let decodedPeople = try? NSKeyedUnarchiver.unarchivedArrayOfObjects(ofClasses: [Person.self], from: savedPeople) as? [Person] {
    people = decodedPeople
}

but it's not working

I think you already discover this, but I'll write here because could help other people. Your code it's just missing the typecast of savedPeople as Data.

if let savedPeople = defaults.object(forKey: "people") as? Data {
    if let decodedPeople = try? NSKeyedUnarchiver.unarchivedArrayOfObjects(ofClasses: [Person.self], from: savedPeople) as? [Person] {
        people = decodedPeople
    }
}

That didn't work for me so I did this instead:

if let savedPeople = defaults.object(forKey: "people") as? Data {
    if let decodedPeople = try? NSKeyedUnarchiver.unarchivedObject(ofClasses: [NSArray.self, Person.self], from: savedPeople) as? [Person] {
        people = decodedPeople
    }
}