It uses WebRTC and tries to do P2P connections.
Note that this leaks your IP to the other caller and vice versa, but it's also quite fast as you can establish a direct connection.
If P2P fails it will try to fallback to your configured TURN server and use that one for relaying.
However not every instance has one (as TURN servers are usually not that modern and straight forward...) and if this is the case it will fallback to Matrix's global TURN servers.
I would recommend Matrix as it has pretty much everything, including cross platform clients, threads, voice/video calls, screensharing, spaces (aka servers), federation and E2EE.
Matrix also has bridges for Discord and pretty much every other service so this could ease transition...
But self hosting requires reading the docs and having some in depth knowledge and understanding as it can be quite complex.
I would recommend just creating a Matrix account on one of the common global servers and testing it.
If you want to self-host there are some pre-defined setups available (example) but I would still recommend to bring at least 5-10 hours.
Regarding operations: It's really resilient and barely ever breaks and also doesn't need a lot of resources. A 1-2vCPU server with under 1GB RAM server is enough for less than 10 people.
US clickbait and ad infested news website directly quotes "trust me bro" Twitter post + describes in 2 sentences what a ramdisk is and does zero real "journalism" like maybe contacting mentioned dutch authorities or Windscribe themselfs.
Once again: Ban Tom's Slopware. Post the original source instead.
Fun Fact: Doesn't really work in Winter.
Source: EU countries that don't have a ton of cheap gas, flowing water or nuclear power and unlimited storage.