One was going to be change the color of completed but you did that in latest 1.7.21 (thanks! much easier to read status). The thing I have needed in my recent use is an ABORT or STOP button that cleanly kills all the processes and returns to main screen (maybe a popup saying you stopped). For numerous reasons I have had to kill it using "Exit" but that doesn't not stop the MakeMKV and Java processes. Requires either killing in Task Manager or rebooting to get to a clean state ready to start again.
PS. maybe a PAUSE too