I have found some kind of temporary solution that solve flickering and framerate drops !
- Find the exe file of Hearthstone in the install directory
- Right click on it, open properties
- go to compatibility
- You will find a button in the settings part. “Change high DPI settings”
- Check the check box about “High DPI scaling override” and select System or System (enhanced).
You can start Hearthstone again, the problem is now gone.
Hope it will be as efficient as it was for me ! 
EDIT : Thanks to Cahrin for the language and check box precisions 