I ended up figuring out the "def unren_noblock(*args, **kwargs):" fix on my own but too bad I didn't check here first because you already discovered it before me.
UnRen also has an annoying UI bug where if you push enter without typing anything in while at the exit menu, it will repeat the last command you typed instead of exiting like it should.
At the very last lines in UnRen, adding "set exitoption=." to assign the variable to nothing fixes it.
Code:
echo Finished!
echo.
set exitoption=.
echo Enter "1" to go back to the menu, or any other
set /p exitoption=. key to exit: