The FireBase\JWT library has been included in Moodle core since Moodle 3.7. The mod_bigbluebuttonbn plugin includes an older version of this library in the vendor directory. It is included to facilitate use of a single plugin version for a very wide range of Moodle versions.
High. The version of Firebase\JWT is old, and no longer supported. It is not required for this plugin to continue working as a more recent and supported version is included in the Moodle LMS product.
Remove the Firebase\JWT library, the vendor directory, composer files, and related code supporting conditional inclusion and use of the library from the vendor directory.
Easy. The code is already conditional and is only included in one location.