Open a private tab
You can see the PBM icon in the notification
You can't

I think this may be related to #13228
So I bisected this and it's a regression of https://github.com/mozilla-mobile/fenix/pull/13481.
R.drawable.ic_pbm_notification was removed and replaced by R.drawable.ic_private_browsing. The problem is the fillColor of the drawable: it's used to be @android:color/white, the now used ressource has ?attr/primaryText as fillColor. Changing this to @android:color/white fixes the issue but since it's also used in other places it's not the solution. The easiest way would be to restore R.drawable.ic_pbm_notification but maybe there is a more elegant solution since the fillColor is the only difference between these two drawables. @NotWoods?
This is also reproducible on Nightly 200831 with Pixel 2 (Android 9).
Android should process non-white fills. I think the issue is that it's not loading any color from the attribute.
This is also reproducible in the latest beta update.
Verified as fixed on Nightly 9/11 and 81.1.1-beta.3 with Samsung Galaxy Note 10 (Android 10) and Google Pixel 3 (Android 11).