Here is what I noticed: if I restart my computer and play the game, the FPS is fine. When I put my computer to sleep and wake it up and play game, the FPS is horrible.
So I restarted my MacBook Pro a couple of times today and it seems to have resolved most of my frame rate issues. Rocket League, Civilization 6 and Pillars of Eternity FPS are almost the same as they were in Sierra. Not sure why it took me restarting my computer 3 times for it work like that.