Performance Issues: Troubleshooting & Solutions

Hello community,
My Skoda 1.9 TDI (manufactured in 2002) has recently started experiencing a significant and sudden loss of power at higher RPMs, especially when going uphill. If you briefly turn off the ignition and then back on, it returns to normal. The error memory contains two messages: "Turbocharger boost control: Limit exceeded" and "Throttle position sensor (G79): Signal too high". The workshop immediately suggested selling me a new turbocharger. When I pointed out that it could be the mass airflow sensor (MAF), they responded that if that were the case, the power loss would occur across the entire RPM range.
Many of the reports here say the opposite.
Could the two error messages be related?
Should I replace the mass airflow sensor (MAF) first? And how do you even find a workshop that won't just try to sell you the most expensive part without properly diagnosing the problem?
Thank you in advance.

Regarding the error message, I would initially rule out a problem with the LMM (likely referring to a mass airflow meter or similar). The error indicates that your boost pressure is too high, which is why the emergency mode is activated after a short time. In this mode, the boost pressure is significantly reduced to prevent damage.
If you turn the car off and then on again, it will run normally until the emergency mode kicks in again.
The turbocharger control unit (MSG) has the ability to regulate boost pressure. Through a pneumatic valve, the variable turbine geometry (VTG) can be adjusted to increase or decrease the boost pressure.
You could also start there; check the MWB 11 module (ideally modules 3, 8, and 11). This module displays the boost pressure and the control ratio of the boost pressure control valve.
If the boost pressure is significantly higher than it should be, the duty cycle should ideally be as high as possible (this indicates that the wastegate is trying to reduce the boost pressure). If it's not, then the boost control valve is most likely defective.
However, your workshop might also be correct; if the variable geometry turbine (VGT) rod is misaligned or the VGT actuator is jammed, you will need a replacement turbocharger.
Here are instructions on how to adjust the VTG (Variable Turbine Geometry) vane (I would advise against it, as this is an extremely critical area of the turbocharger), or how to temporarily free up stuck guide vanes. Simply search online; in most cases, this will only work for a few weeks before the problem recurs.

Is the car tuned?

You should check the G79; perhaps something got interrupted. Are the errors still present after deleting the files?

The car is not tuned.
If the VTG (Variable Turbine Geometry) is misadjusted, wouldn't a power loss always occur?
Der Wagen hat aber seine "schlechte" und seine "gute" Tage, wo ich das Gaspedal durchtreten kann und selbst bei 170 noch einwandfrei läuft. Für mich klingt das irgendwie nach Elektronik, vielleicht ein Sensor. KCan that be it?
"Additionally, the car sometimes experiences slight dips in power during acceleration (around 100-110 km/h), but the emergency program does not engage."