A stall warning only comes up when you’re… guess what… stalling or being close to that. I relates to the angle of attack.
Look for the best climb speed Vx for your aircraft and hold it. Don’t climb with the VSI as a reference, only use speed.
MSFS has a very (VERY VERY) bad and entirely wrong implementation of mixture and since Carenado stubbornly uses nothing but default system I would recommend to activate automixture for such an undertaking.
This so called “cervice ceiling” doesn’t mean that your aircraft can always reach this altitude. It’s just certified for it. It depends on various factors such as weight, temperature, in reality even the quality of the fuel. But it also means that the aircraft can technically reach even higher altitudes, depending on [see above].
Fly on speed, that’s critical… If you get slower your angle of attack becomes higher which will increase your drag and you will possibly not be able to recover from that except by pushing the nose down which will likely result in a descent.
And… well, you got it yourself… Don’t expect a correct flight model from Carenado.