Part of the screen record solution - iPad Pro 12.9 M1 2021

Hi.

I'm looking for an app that allow to record only a part of the screen on my iPad.

I do not want to use another device to accomplish that.

The crop solution lose quality and it not quite suitable for what we need.

Is there a workaround?!

Third-party apps ... I try a lot of them but none allow me directly to select a part of the screen that I need to record.

We use the records for hand written math lessons.

Best regards.

Fabian