All devices like android and ios are 100% firewalled, blocking ALL incoming, unsolicited traffic. No way around this without rooting.

So no, it’s not possible as you’ve described where it is strictly peer to peer with no server involved.

But there is some hope. Apps like Nextcloud Talk use a server, but are 100% open source, free, and hostable on a LAN. And matches what you’re after feature-wise.

You encapsulate the awesomeness of the open source community with this content. Thanks for sharing!