If you receive that error in the webui, you’d likely also receive it using mineos_console.py. For screen to report “none” means that screen couldn’t be found in the $PATH variable.
After installing screen, it might not immediately solve the problem depending on your system, if hash is not run (either manually or automatically). Hash basically looks at directories (in this case, /usr/bin) and hashes the file contents quickly so it knows if any files are added/removed.
If it’s not run automatically, it’s typically solved with a reboot, then you should be able to operate all functions normally from the web-ui/scripts.