How to install any app as a parallel app in OnePlus 6?

OxygenOS in some OnePlus devices allows its users to create a clone of an existing app using a feature called "Parallel apps" under Settings app. The problem, however, is that only a handful of apps are listed as "eligible" to be run in parallel. As a result, the user has to resort to third-party apps to run an app of their choice in parallel. To make a case here, "Firefox for Android" cannot be installed as a parallel app! I'm looking for a workaround for this superficial limit of only eligible apps to be run as parallel apps. Note: I am using a OnePlus 6 running OxygenOS 10.3.2 (Android 10) with Magisk and Riru.