I make 3d Avatars for VR applications like VRChat and VSeeFace as a hobby.
You can view them on mars.squirrel.pub.
The single relevant format for VR & V-Tubing avatars is a .unitypackage that contains a scene with a setup somewhere.
There is no interoperability for avatars, and it is severely lacking for 3d models by themselves.
Using those avatars as an end-user is prohibitively difficult, as it requires the use of a Game-Engine like Unity.
I'm trying to improve that, by creating a truly extensible file-format for 3d models, with the capability to be easily extended with VR avatar functionality, that is agnostic of any game-engine or application.
With such a format existing, an end-user friendly character-editor application could be created. Users could create their VR & V-Tubing avatars once, without the need for technical knowledge, and be able to use it everywhere.
You can view my progress in the STF - Scene Transfer Format Repository