The original RARBG RSS feed link followed this general pattern: https://rarbg.to/rssdd.php?/rssdd?category=movies
Go to the RSS tab (usually found in the "View" menu in qBittorrent). rarbg rss feed link
Assuming you have found a working feed (from a clone or an alternative like TGx), here is how to set it up like RARBG. The original RARBG RSS feed link followed this