Hi Tony,
I came across your post because I was having similar issues selecting R2FX while running WxtoImg on the Pi. I just started running it on the Pi after running it on Windows for years. ?I know it has been a few months since your post but I have a solution for you, albeit a tedious one.
You can hold shift and click on the receiver selection and that should hold the drop down menu so that it is visible continuously. ?Then select the R139 receiver and with your keyboard arrow down 2 times. That will select the R2FX. ?Hit enter and you should see that R2FX is selected. I had to look at the Windows version to see how far down the R2FX was from the R139.
I know this is not a complete solution but it’s the best I can come up with for now.
73.
Clint, KC9S
