Unless your server is hosting other websites then it should be a closed server and you shouldn't have to worry about anonymous people getting access to it if it's not the free Jitsi portal version that's using Jitsi server

We are literally hosting social networks. Thousands of users. Not exactly "anonymous".

I am posting a valid concern: anyone can open video chats on our server by visiting the URL of the subdomain. Request - how to make it so that nobody can do that, and jitsi is only accessible through that UNA popup.