Since no additional recommendations from the forum. I took it to my local mechanic have been using for 20 years.
They replaced the Camshaft Position Sensor (Exhaust) and said he repaired some wiring /fuses stuff and now engine lights are gone and surprisingly the ac is working again. Hope this will ...

Disconnected the battery overnight +12 hours. Started the car and let run a few minutes, no check engine light yet. Drove 10 minutes streets turned off. When turned on the check engine was back, drove 10 minutes on highway. The performance seemed almost flawless no stumbling and was able to ...

Added to the S60 side of the forum recommendation per one of your contributors. Since apparently the XC90 has fewer much fewer views. Here it is:

Volvo XC90 2008 3.2 - 77,000 miles only basic mechanical maintenance until now no significant problems with car before but now ....

Engine Stumbles ...

Volvo XC90 2008 3.2 - 77,000 miles only basic mechanical maintenance until now no significant problems with car before but now ....

Engine Stumbles / Lacks Power / some Knocking/ RPM can run high and engine will lag to change gears.

Recent History
2 Months Ago - Battery Draining and died ...