>>288647980
https://www.youtube.com/watch?v=9fgkpM6211w
https://assetstore.unity.com/packages/tools/camera/vr-tunnelling-pro-106782 has a bunch of motionlet mitigation techniques implemented, with basic vingette and some "cage" effects as well. I can't speak to their effectiveness since I don't get motionsick, but you might be able to dress up the cage effect to be on-theme for sonic somehow.