When you mute someone, you may want to still see visemes on their avatar working because you are in the same voice chat with them or communicating otherwise outside VRChat. Currently the only workaround is to set their individual voice volume to 5%, which is not ideal because their voice can still be heard a little. Also, after a recent update it is now possible to go past 5% volume down to 0%, which effectively mutes the person and their visemes stop working as if they were muted with the toggle.

I suggest changing the 0% voice volume behavior from "the same as mute toggle" to "no voice is coming from them, but visemes are still working".