Games/top is sorted by viewers already. It just doesn’t return the view counts in the response
If you wanted the actual view counts
You’d have to call games/top then call streams filtering by game_id load a a few pages and math it up yourself.
So call https://api.twitch.tv/helix/games/top
Grab a gameID (so Just Chatting is 509658)
Call https://api.twitch.tv/helix/streams?game_id=509658 load a few pages and add up the viewer_count
Generally speaking, for various reasons Twitch no longer calculates the totals of things for you, so you have to math it yourself.