If you’re using jellyfin as the url, that’s an easily guessable name, however if you use random words not related to what’s being hosted chances are less, e.g. salmon.example.com . Also ideally your server should reply with a 200 to * subdomains so scrappers can’t tell valid from invalid domains. Also also, ideally it also sends some random data on each of those so they don’t look exactly the same. But that’s approaching paranoid levels of security.