I'm not sure if any light has been shed on this topic. I found myself in the same boat as all of you recently, as i have severe frame issues when previewing my stream. When I finished searching through several forum posts and finding that this hasn't been implemented yet, I started looking for workaround to this.
After a short time, I figured out a simple fix until this is eventually implemented.
First, go to Settings > Hotkeys
- I simply assigned a hotkey of "Enter" on my Numpad (Anything would work, obviously that isn't being utilized) to the Studio Mode spot.
This will simply toggle Studio Mode, showing you a quick preview of your stream, and then you can simply press your hotkey again to go back to disabled preview!
I hope this helps you, my fellow streamers, content creators & personalities alike!
If you would like to see screenshots of exactly where to go, you can check the attached images.
If anyone has a better workaround or knows of a newly implemented way to hotkey enabling/disabling preview, please let us know!
Best of luck!