I am plugging an AtomS3U into a USB port of my Windows 10 laptop and I want to have the AtomS3U emulate my microscope. To do that, I need to send and receive serial characters.

Completely new to the AtomS3U and UIFlow2, I have just recently managed to get my first progam into the AtomS3U and that works: able to change the colour of the internal LED.

Now, I want to be able to read and write data on the PCs USB (COM9) connector.

To test, I am successfully using Putty to talk to COM 9. (115200 baud, 8 data bits 1 stop bit, no parity) Flow control. I have tried with and without XON/XOFF.

I see Hello World messages from the Atoms3U showing that I have the correct COM port and that the AtomS3U is programmed and working. However when I type something I never see any data available message showing communication works from PC to Atom.

Why can I communicate in one direction only?

How do I get a "Hello World" program into an AtomS3U 8MB?
I seem to have found UiFlow2.0 online and had to register.
(I hate that, Why can't I buy something and then do what I want with it anonymously?)
(I didn't want UiFlow, but the thing I couldnt get it to work work with the Arduino IDE the way all my other Microcontroller devices seem to work quite easily, with SetUp and Loop, once the device type has been set.)
I have downloaded run M5Burner-v3-beta-win-x64.
(I dont see why the uploader isnt part of the IDE, but it seems thats just how it is.)

Now I think I have told UiFlow2 that I have an 8MB AtomS3U and put some M5 something into it and given it a name "testAtomS3Uivan". The thing shows red with a big question mark as if something is seriously wrong.
There's a large button on the top of the AtomS3U. Pressing it does nothing. At times in the past it made it light up red.
There's a little button on the side. Pressing it makes makes a small green LED in the corner light up, while pressed.
Windows device manager finds a USB Serial Device on COM 3.

Any advice on getting a "Hello World" program running?