Had a look at a pretty good video for the Autophix OM126P, it showed it for American IM readiness, looks like you get a lot for around £30 and nicely designed, one vid had you get free lifetime updates I don't know if that applies to UK or not, freeze frame and live data will be useful. - https://www.youtube.com/watch?v=SsfvtdCTukk
Usual advice with code reader make sure it is fully updated before you plug it in. The limits might be that this is a generic code but the vehicle has also registered an issue by throwing up a couple of warning lights.
P003A -
"What Does the Engine Code P003A Mean?
Character "P" in the first position of Diagnostic Trouble Code (DTC) represents the powertrain system (engine and transmission), "0" in the second position means that this is a generic OBD-II (OBD2) DTC. "0" in the third character position in a DTC indicates that the fuel and air metering and auxiliary emission controls is experiencing a malfunction. The last two characters "3A" is DTC number. OBD2 Diagnostic Trouble Code P003A means that Turbocharger/Supercharger Boost Control 'A' Position Exceeded Learning Limit has been detected.
How Serious Is the Code P003A?
This issue is critical and can lead to damages in your car. Please clear it first, drive your car for a couple of days. If the issue reappears, Carly recommends to fix your car to resolve this issue." - https://www.mycarly.com/obd-codes/p003a-turbochargersupercharger-boost-control-'a'-position-exceeded-learning-limit/
Have you driven the car and put it under a bit of load say going up a hill or pushing the turbo with higher revs in a gear higher than you should be in to see if it's under performing? Car running well being a VW always makes me think of potentially computer brain-farts and perhaps electric, wires, connectors etc.. Did you delete the error code after the old off-'n'-on-agen failed? A higher level scan tool might give more info and detail. - https://www.youtube.com/watch?v=LCDvnHKM6m0
The alternator can't do much if the car's not running, 70% /12.35v isn't low (particularly if you go with the 12.4v / 80% but why not fully charge the battery to 100% with an appropriate battery charger maintainer following the instructions for the car in the Owner's Manual and for the battery charger maintainer and recharge at a lower rate (of amps) over a longer time as possible. When the car has an issue(s) it's best to have the battery in the best state of charge possibly, particularly if the issue involves computer, electrics, engine starting as this can help with diagnostics and repairs whereas a low state of charge can hinder diagnostics and repairs. (I know you know this, put for other readers.)
ETA: IIRC(?) throttle body issues were generally with 2019 cars