The best options for you are going to be SimpleX Chat or Jami, depending on your use case. If you only need to make video calls, probably Jami is the easier option, but if you’d like to have a chat app with video call support, SimpleX is the right choice. SimpleX is also just a really good messaging app, because it has no user identifiers or accounts. They have a wonderful explanation of their method for two-way communication in their whitepaper if you’re interested.

Also, video calling in a “secure environment”, as you’ve stated, is not difficult and certainly not impossible. There are plenty of options available. Others beyond the ones I gave are Jitsi (but it’s gone way downhill; don’t use it), Signal, Element (you do NOT have to self-host for it, you can use the main instance or any other instance), and the options open up to basically everything if you make a new user profile and install sandboxed Google Play Services in the new user profile (from the “Apps” app). With sandboxed Google Play, you can use apps like Zoom if you really wanted, but I’d strongly encourage you not to for the sake of privacy. You can download apps without signing into a Google account via the Aurora Store.