If Pep and Manchester City were able ti sign defenders this January, they will be better than they are right now, and they can still compete for the title race.
I don't think anything can bring City back into the title race, right now they have to look at other trophies and try to finish in the top four in the EPL, they are too far away from Liverpool, and Arne Slots team is not looking like slowing down at all.
That said, City are already busy in the transfer market this month, they want to sign a couple of players, they are close to signing Victor Reis from Palmeiras, Khusanov from Lens and Omar Marmoush from Frankfurt, these are good signings that will help City, both now and in the future.