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I think bounce.io with a group of staffers would probably be a fun, intuitive and harmless game for him to try out. Keep talking and nobody explodes would be good as well.
I guess difficulty and optics are what matters the most. It would be hilarious to see Bernie play Crusader Kings 2 or Tropico IV, but then it wouldn't look very well.
Anything multiplayer should be played within a closed group only imo, to reduce the chance of edgy usernames popping in on stream or the odd streamsnipe happening.