its very easy to install via docker as mentioned above. Mumble is very lightweight. You could run the server on your desktop in the background easily or even on your router, there is a package for openwrt. The sound quality is awesome, voice is e2e encrypted and bandwidth should not be a problem either for a couple of people in the chat while you are playing.
Exacly, these popups are completely unnecessary and just a form of malicious compliance by the website creators.