QGIS is actually one of the big portable/cross-platform hybrid Python/C++ apps, which makes it arguably more complex for an LLM to cope with properly than one or the other, and makes code quality a rather more entrenched/storied problem.

In this way it is very much a spiritual cousin of FreeCAD (also cross-platform Python/C++/Qt6), though that (at least currently) has a somewhat more liberal ("humans in the driver seat") policy.