Hello there,
Have you made any recent updates to the device?
-In settings open the “Corners and Edges” feature.
-Now you will need to search for the “Allow switching between recent apps” and turn it ON.
-Now restart the device, When the device starts check again if your alt + tab feature works correctly in your Windows operating system.
You can also clean boot the device or boot to safe mode and see if that helps .
Hope this resolves your Query !!
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