How send data from UNO R4 to windows (python)

Official Hardware UNO Family UNO R4 WiFi
5

If I understand your code, you wish to receive data over the network. Before doing a

client.read();

You should check to see if any data is waiting to be read. To do this, you might do something like this:

while (client.connected()) {
      if (not client.available()) {
        continue;
      }
      char c = client.read();

Perhaps you could provide a better description of how your code is supposed to work. It may be easier to forget about HTTP initially, use a Python socket to interact with the Arduino, and then convert to HTTP when everything works.