Right if boost pressure is flagging as high I would do the following...
Clean the MAP easy to do.
Clean the VGT actuator rod and mechanism and grease it these can stick and over boost would be caused if stuck in small turbo mode.
After that I would get someone to start car and turn it off a few times look at vgt rod and make sure it moves about 1cm when you turn car on and comes back when you turn it off....
If it doesn't move so easily or looks like sticking then I would clean vgt solenoid there was a thread on here recently with a polish guide to cleaning it (pictures in guide so easy to follow) be careful taking vac hoses off it.
Lastly clean EGR anyway though unlikely cause of this problem they always need cleaned
and can really effect performance.
If that hasn't sorted issue then I suggest MAP sensor could be faulty or vgt vanes in turbo could have got clogged a little. Turbo off to clean but don't think it's too big a job. If you had a cable and ecu software you could watch map sensor data at idle it should read near 1 bar. You could also graph desired boost against actual and rpm to see if your getting boost the ecu wants or not.
If mucking about with vgt solenoid anyway I would replace the rubber and plastic hoses with silicone ones as these do crack and even though mine weren't leaky it feels like it had better control since changing them. Should only cost you a few quid for hose. I was recommended 3mm and 5mm on here but I found 5mm felt too loose on solenoid and vgt actuator so used 5mm from pipe on engine to solenoid but slipped a little 3mm inside solenoid end of hose to make a snug fit. Doing again I would probs just use 3mm.