The released version of the KoboTouchExtended driver will not work with calibre before v5. It uses features of Python 3 and calibre that are not in the older version. You can get older versions of the driver and related plugins from
https://github.com/jgoguen/calibre-kobo-driver/releases. Version 3.2.15 should work with calibre 3.48.
There are two choices of what you can do.
The first is to use the version of the KoboTouch plugin linked by @PeterT above, named KoboTouch348. This will allow calibre to manage the Libra 2. Then, use the 3.2.15 version of the Kepub Output plugin and convert the books to kepub before sending them to the device.
The alternative is to edit the version of KoboTouchExtended driver work with the Libra 2. That means changing it to inherit from the KoboTouch348 driver. Or adding the device lines in that driver to the KoboTouchExtended driver.