Here's one way to do it...

//get your JSON data from wherever
//for this example, I just used a static string
let json = """
{
    "customers": ["Example", "another"],

    "projects": [
        {
            "project_name": "Website",
            "customer": "another",
            "timer_progress": "0:34:23"
        },
        {
            "project_name": "Logo",
            "customer": "another",
            "timer_progress": "0:58:56"
        },
        {
            "project_name": "Big Project",
            "customer": "another",
            "timer_progress": "5:23:56"
        }
    ]
}
"""

//this is how we tell Swift what format our raw JSON is in
struct DecodedJSON: Decodable {
    let customers: [String]
    let projects: [[String:String]]
}

struct ContentView: View {

    @State private var customers: [String] = []
    @State private var projects: [[String:String]] = []

    var body: some View {
        Button("Load JSON") {
            loadJSON()
        }
        //so we can see that the data loads
        .onChange(of: customers) { _ in
            print(customers)
        }
        .onChange(of: projects) { _ in
            print(projects)
        }
    }

    func loadJSON() {
        //depending on where your JSON is coming from,
        //you should do the necessary set up steps
        guard let data = json.data(using: .utf8) else {
            fatalError("Could not convert JSON string to data")
        }

        //here's where the actual decoding happens
        do {
            let decodedJSON = try JSONDecoder().decode(DecodedJSON.self, from: data)
            customers = decodedJSON.customers
            projects = decodedJSON.projects
        }
        catch {
            print(error)
        }
    }
}