Is that question regarding accessing Pega app on mobile using plain browser (Chrome, Safari) or PIMC mobile application (built from the Mobile Channel)?
My below response is applicable when the answer is PIMC app.
Please create a Mobile Channel when being logged as an Author on UIKit-based app and build your app (iOS/Android) from there. I assume you have two separate access groups for end-users 1) UIKitBasedApp:Users 2) CosmosBasedApp:Users. Please make sure that for end-user operator records both AGs are configured, and Cosmos-based one is configured as a default one.