This isn't true full participation for everyone, but I wonder about tools like Google's LiveTranscribe. I've tested it in a very loud room (multiple conversations) and as long as I hold my phone's mic quite close to me, it only transcribes me. So in person students could do that and their contributions could be added to the class chat for the online people to at least read, if the mics aren't picking up the in-person students well.

we're contemplating using CARES funding to get all students a pen tablet (likely a ~$30 one, for annotating and the occasional handwriting, not for artistic drawing). I think of that as a game changer but I recognize my physics background (it's great for equations and diagrams, of course) may be dominating that thought. Would it make a significant different in your opinion?