Maybe this is of any help: Nextcloud HPB: Talk / Signaling - Server v. 2.x - Carsten Rieger IT-Services
It’s in German, but Google or deepl should be able to help with that if German isn’t your native language.
Oh, and be aware that it needs a dedicated server somwhere in the ball park of 4 CPU Cores, 16GB RAM und 1GBit/s networking (actual rescource usage may vary depneding on the number of participants in a call).