So I have a viewport frame with a World Model that has a model inside of it of an r6 character and what I want is that the r6 character would play an animation inside of the viewport frame
You can't, but you could try playing an animation in a rig that ins't parented to the viewportframe and make a loop that changes every part's cframe to the rig that is currently playing the animation
You should use WorldModels to play animations, they allow for some physics to work in ViewportFrames. To be honest, I'm not completely sure how to use them, but here's the API documentation. Hope it helps :D
https://developer.roblox.com/en-us/api-reference/class/WorldModel