The yellow lamp with the glow plug symbol doesn't actually indicate the preheating process in TDIs anymore.
It is, rather, a general motor control indicator light.
Later, after about 200 uses, the MIL (Motor Indicator Light - something in English) also came on.
If a "1Z" indicator light illuminates while driving, it means something is not working correctly.
It indicates a malfunction of a component in the engine that is being monitored by the self-diagnosis system.
It could also be related to the ABS (Anti-lock Braking System), so it's advisable to check the engine and ABS systems, evaluate any error codes, and then take appropriate action.