~Snip~
The truth is that once Manchester City get their form back, it is possible they will focus on both the Champions League and their domestic league. However, if Guardiola notices that they are still in average form, he will definitely prefer to focus more on the Premier League so they can finish in a better position in the league table, ensuring Manchester City qualify for next season's Champions League.
Now the question arises, when will they return to their best form?
Currently City are like toothless lions who are having difficulty beating their opponents, they were not even able to beat Everton, let alone when facing a stronger team in the UCL. If Guardiola is able to improve his squad after taking advantage of the January transfer window, he must focus more on the domestic league to be able to compete again in the top four. I'm not sure City can survive much longer in the UCL, they will definitely lose when facing the favorites.
Citty match against PSG will determine if they can survive the group stage. If they fail to win PSG, they are gone. It's only the transfer window that can bring back hope to City because their current players have nothing to offer again for the club. EPL is the only league that City can be hopeful of and that depends on the team's strength after getting new players in January.