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Thank you for bringing this up. However, at the moment, there’s no official confirmation from Microsoft that the Windows + Shift + F shortcut has been removed or changed. This key combination is documented for selecting the screen area, but it may behave differently if intercepted by Windows or other apps.
In the meantime, I recommend way to select a custom area is:
Insert > Screen Recording > Select Area
This will display a crosshair so you can drag and define the region before starting the recording.
Reference: Record your screen in PowerPoint
If you encounter any issue or have other question, please feel free to reach out. I am happy to assist
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