Would brake squeal not also happen under normal braking not just when turning? And slow turning you wouldn't necessarily use the brakes? Just asking
No - Not necessarily.
Although the pads have released from the disc when the handbrake / foot brake has been released, the running clearance between fiction pads and the steel brake disc is extremely small.
The squeal can be produced as a result of slight surface rust, that has formed on the face of the steel brake disc.
This type of squeal is more evident when the car has been sitting, say overnight and it has been damp / wet conditions due to the weather.
You release the brake and slowly drive from your parking space / driveway etc.
This is a likely time to hear may hear a high pitched squeal as the brake pads drag across the surface of the steel brake disc, producing the squeal.
It’s a similar situation when you are making a tight turn around a roundabout.
The extra load on the wheel can cause the pad to make very slight contact with the disc.
You may find that this problem self corrects itself after the brakes have been used a bit more often.
If it gets worse or it does not rectify itself after a bit more use of the brakes, then mention it to your dealer.
Oh ……. You could try reducing the strength of your Regen for a few days.
This will mean you will be using your footbrake more often, which will help clear any surface rust from the brake discs.