Answer:
BPS already does that by default (see the BPS default root htaccess code below). So you don’t need to do anything else to disable directory listing/indexing.
# DO NOT SHOW DIRECTORY LISTING
# Disallow mod_autoindex from displaying a directory listing
# If a 500 Internal Server Error occurs when activating Root BulletProof Mode
# copy the entire DO NOT SHOW DIRECTORY LISTING and DIRECTORY INDEX sections of code
# and paste it into BPS Custom Code and comment out Options -Indexes
# by adding a # sign in front of it.
# Example: #Options -Indexes
Options -Indexes