2019 crosslandx with 50000mls smoking only smoking after long engine braking. The pcv valve has been replaced but didnt cure it now suggested a piston ring clean for 550 pounds. I am using a main dealer who I am fast loosing confidence in.

I would say that unless it is excessively smoking and it is clearly engine oil being burnt (oily exhaust pipe at the tail end) and the oil level is dropping then it may be a case of running it in until the rings bed in.
Ensure that it is running the correct grade of oil and also run it on Supreme fuel which does make a difference.