Big write-up on Harrison in the Athletic. The gist is that he's well above the U18's level and was visibly frustrated by the lack of quality, dominating in the FA Youth Cup match, and that Moyes is impressed. They suggest that he could already step in and take over Doucoure's role with more creativity, but that some at Everton would rather see him go out on loan and continue to develop.
If you search for Everton from Google News and click the link there, it seems to prevent the paywall that comes up when going directly.