I created a bootable usb drive with ubuntu so that I would not affect my main windows laptop drive.  However, using it corrupted my windows drive such that it needed complete restoration. This happened twice.  I changed from UEFI to legacy boot to boot the usb.  And changed it back when I tried to boot the windows system.

Can someone guide me on how to create/use an external bootable drive with linux such that it does not corrupt my windows disk?

I have a dell precision 7540.

Thanks