Maybe he could get one of those Razer respirator style masks they made some limited runs of. Both because RGB for a gaming related lawsuit, but also because they made a point of making the mouth area clear so you can see the person's lips moving when they were talking. That or one of those Dyson headsets that has the air filter thing, but it would cover the lips from view. I am sure a mic of some sort could be added if their claimed issue is about being able to hear him clearly.

Also I don't see how Valve could lose to an antitrust lawsuit in this case. They do have the most "name brand" storefront for PC games. They aren't like Apple, Microsoft, Google, Sony, or Nintendo with regards to being either forced to use services and all the shit that Microsoft, Apple, and Google pull with their OS'es and products really really not making it easy to use options you want to (if the option is even present). And they aren't stopping you from playing games from other storefronts or media (like direct downloads from the studios or from physical media), they even let you add non-Steam games to the launcher and don't tend to stop you from modding. It isn't like GOG, Epic, EA, Battle.net, Microsoft Store, etc are some tiny unknown options that most gamers are not aware of.