Have you checked in the Window list of panels?
Window/Lumetri Scopes ...
Hi, I recently had the same issue and called Adobe. They had me install Premiere 2019, and it now works.
It sounds like the 2020 version changed system requirement, and my 2012 MacMini no longer meets the minimum requirements. But, as mentioned, having both versions installed now allows me to go back to the 2019v to use the scopes.
hope that helps!
Unfortunately, about every five years you should definitely look into replacing your computer. I think in 8 year old lower end Mac is out of specification for the current application and OS combination you are running.
Please tell us your system specs: OS version, Premiere version, amount of RAM, Hardware specs including graphics card. but as jonathand42542032 said, your system probably doesn't meet the requirements for premiere 2020. There have been other posts here reporting this and I've had this experience on my older macs...