Sicario2 he hasn’t really stalled just Artera stopped playing him entirely
Those things are most likely linked.
We're fortunate in that Lewis Skelly and Nwaneri came into the team at roughly the same time. Lewis Skelly made himself a mainstay and has become pretty much undroppable. Nwaneri, for some reason, couldn't. Might be attitude, might be what Arteta sees on the pitch, might be how he trains. But it's something he needs to work out.
To add to what Jazz just said, he might just not be physically ready in the was Lewis Skelly is. Could just be a timing/development/growth issue.