Suspect that may well be an Obdeleven / VCDS mod.
You get a beep if in gear with seat belt off.
It feels like this one on the Obdeleven thread:
Either my search isn’t working or this hasn’t been touched on yet. Replaced my totaled 2016 GTI with a 2019 and it has a new audible and MFD warning when the driver door is opened while the ENGINE
forum.obdeleven.com
Don't know whether you are into the joys of twiddling with Obdeleven (*)... got a thread on that on the standard
Ateca side. That I suspect that is your solution if there is no menu option which I doubt. I've left my safety feature sounds as is but as said that isn't one I get. It's a DSG, I can wander around outside with the engine running door open no beeps.
(*) other VCDS tools are available but best to stick with the programming type rather than the per app type. Pro version of Obdeleven rather than the app version or those other dongle devices. Need an Android phone / tablet. You can use the sponsored Amazon reader Android Tablets for a cheap option if technically minded.
Mind you not sure whether they sorted it out on that thread but there will be others. Mind you on that thread when they talk about the app credits why you do it with the Pro version, no costs attached to twiddling with stuff and you are doing it directly.
I start off with a Google like this then search for a coding mod that you then find in the Obdeleven screens:
Mind you it might be one of those things that VAG dont want you to change. Something for the winter nights perhaps.