I have the same issue just got it today. I found a work around so you can watch Twitch in fullscreen without the flicker. Hopefully this solves the op's issue. User profile for user: pbergesio pbergesio. Dec 8, PM in response to nick.
Penny. Age: 27.
Apple Watch Speciality level out of ten: 1.
Vera. Age: 31.
Flashing Loop Animation Video Maker for a Starting Soon Twitch Screen
Tried other things including the solution in this thread about Adobe but nothing works. For me the best solution was the official twitch desktop app. I do not get the flickering while using any other streaming services with Safari. User profile for user: pbergesio pbergesio.