Ideally you need to get the car scanned with VCDS. There might be other codes logged that can help pinpoint what’s going on.
My experience of turbos, 2012 A4 Allroad with under 70k miles went into limp mode. Ordinarily I would have stripped it down myself, but pointless cleaning, given labour to get to it. The exhaust manifold nuts can be a sod without induction heater. In addition the oil feed pipe to it needs to be replaced as the union nut rarely goes back on properly, and this is usually down the back of the engine. Bypass this and you risk an oil leak. There’s also an actuator on there. This is normally set up with the turbo on the bench. It can be tested with a vacuum.
Any cleaners likely to be short lived. When I stripped the turbo down on mine it had carbon build up. Also one of the vanes on the turbine was bent. Normal to do oil and filter change as a matter of course when fitting.
Check out Turbo-diesel.co.uk. They will have Garrett turbos, BorgWarner, new in a box, or you could opt for refurbished. Main dealer will use exactly the same part but boxed Audi and daft price. You’ll also need exhaust gasket kit.