Well leaving so many blanks, one can’t help you. Setting it up for my own instance was as simple as setting up web RTC. As for other instances, most including the flagship should have it enabled by default.

What setup doesn’t allow it?

XMPP clients: https://de.wikipedia.org/wiki/Liste_von_XMPP-Clients

?

We run matrix voice and video calls daily on a self hosted federated instance. It’s a non issue.

XMPP and Matrix exist, “hey let’s reinvent the wheel”