An injury problem will be having more than 3 of the first team players out with injuries. Take Barcelona for example, they are without Lewadoski, Raphina, Pedri, Frankie Dejong, and Kounde. City can cope without Kevin.
Manchester City's performance is a little different when De Bruyne and Rodri are not in the squad, but if one of them is there then Manchester City's performance is quite good. It may have happened by coincidence, but Manchester City has always had difficulty winning matches without its best midfielder.
I miss De Bruyne's performances and I hope he can return sooner than scheduled. But of course his performance may be different because of this long injury. Kovacic and Rodri make a good tandem in Manchester City's midfield without De Bruyne, but of course De Bruyne is still expected. Raight now Manchester City is still having difficulty penetrating the Young Boys defense, but they really dominated this match. I hope in the second half they can break through Young Boys' goal with 2 goals.
I'm not sure about Rudri, but I'm pretty sure that De Bruyne was an effective player in Manchester City, and just like you I miss seeing the performance of De Bruyne in Manchester City.
Maybe the reason of why Manchester City can't have a good performance like we saw from them in the last weeks of the last season is the absence of De Bruyne in the squad. But when De Bruyne gets recovered and starts playing for Manchester City again we can expect to see some improvements in this team.