I'm also using Xcode 12.0.1 and I also accepts its takes a lot of time to when it hits a break point to appear the variables view

Deleting VALIDARCHS=arm64 is the only thing worked. Other solutions like Set Build Active Architecture Only to "Yes" even for release mode. Navigate to Build Settings of your project and add "Any iOS Simulator SDK" with value "arm64" inside Excluded Architecture_. are useless and lead me to another error like this: - https://developer.apple.com/forums/thread/129771 The file “Myapp.app” couldn’t be opened because you don’t have permission to view it. So don't waste your time. Because when you create a new app in Xcode 12 you will not find "VALID ARCHS" key in User defined section which is deprecated. The Build Settings editor no longer includes the Valid Architectures build setting "VALID ARCHS", and its use is discouraged. Instead, there is a new Excluded Architectures build setting (EXCLUDED ARCHS). If a project includes VALIDARCHS, the setting is displayed in the User-Defined section of the Build Settings editor._