Modifications to the > layout engine must not be performed from a background thread after it has been accessed from the main thread

Your network fetch code is almost right - you are reloading the table on the main queue but not stopping the activity indicator.

You just need to move that line inside the closure:

let downloadedData_user = try decoder.decode(Top_us.self, from: data)    self.Top_Search = downloadedData_user.users    DispatchQueue.main.async {        self.tableView.reloadData()        self.Indicator.stopAnimating()    }

Note that by convention, properties should start with a lower case letter while classes should start with an upper case letter. Both should use camelCase, so Top_Search should be topSearch, Top_us should be TopUsers and Indicator should be indicator.

For anyone having problems pinning down the cause, try the following.

Click on your scheme (next to the stop button), then Edit Scheme.

Under Run -> Diagnostics you have to activate Main Thread Checker.

As indicated by the breakpoint that got added, your execution will now halt when you try to alter the UI on a non-main thread.

You should wrap handling error by DispatchQueue.main.async{}

func Download_ID() {    let urlString = "https://www.instagram.com/\(self.username_String)/?__a=1"    guard let url = URL(string: urlString) else { return }    URLSession.shared.dataTask(with: url) { data, urlResponse, error in        guard let data = data, error == nil, urlResponse != nil else {            // Add DispatchQueue            DispatchQueue.main.async {              print(error)            }            return        }        do        {            let decoder = JSONDecoder()            let downloadedData_user = try decoder.decode(Website.self, from: data)            // your logic            DispatchQueue.main.async {               // update or reload table in here            }        } catch {            // Add dispach_queue            DispatchQueue.main.async {              print(error)            }        }    }.resume()}