Sierra 10.12.1 is expected out soon. I expect we might see it by the Apple Event on Oct 27. It's a big update with lot of fixes. Be sure your add-ons are also updated.
The last public beta build today was big 1.25 GB. It took quite some time to download and the install time was similar to installing Sierra. After updating, I would restart a second time in Safe Boot mode then restart normally. As always, backup prior to upgrading.
If the flickering continues after the update, be sure to let Apple know via feedback.
Safe boot
* shutdown
* start the Mac and *wait* for the startup chime to sound
* after the sound, press and hold down the shift key
* keep holding and *wait* until the grey Apple logo appears
* now release the shift key and just wait (it could take a few minutes)
* eventually the login screen appears with the words SAFE BOOT
* simply restart normally