It seems unlikely that FB would give up on Litho, which is extremely performance focused, to use react native instead. Not for their bread & butter flagship news feed anyway https://fblitho.com/
First, both Litho and React Native build on Yoga so there's a fair amount of code sharing.
Second, they serve different purposes. Litho will be used for FB scale optimization of certain intensive views. React Native is used for fast developer productivity. I'd wager that RN will be used in most places and Litho is used in hot spots sparingly.
If I’m wrong then I’m happy to admit it. I don’t follow that ecosystem closely and was only going off a few old blog posts I remember and everyone making a big deal of it at the time.
The Ads Manager app is written in React Native.
The Instagram app is written in React Native.
The entire FB app is not written in React Native yet, but overtime I'd expect more things to be.
The statement that FB "abandoned react native on mobile" is demonstrably false.