2012 Ford Focus 2.0 engine, with code P090C, Clutch B actuator control circuits low, does mean I need a new transmission?

The car acceleration during driving is lagging, it's like it does not take off normally, and reverse goes out, until I turn the car off for a while then on again, it responds normally for a short time

Just because some high school drop-out parts store clerk read a code on his little machine DOES NOT mean that's what is wrong with your car. Take it to a REAL mechanic who can actually troubleshoot your problem and come up with a REAL solution that can be fixed.

This is definitely a job for a dual clutch expert. Ford has been having massive trouble with that transmission, a couple things in the clutch (including gearbox leakage into the clutch) and bad solder connections in the Transmission Control Unit. My guess is it will be the TCU but I would not bet at all.

Ford seems to be taking the tack that "If it affects all the units it is not a defect, it is an unadvertised feature."

Check the fluid level first before you blow big bucks