you need to change bios back to UEFI mode to boot into windows 10
UEFI matches the GPT format your win 10 install is on. It uses the Windows Boot Manager to find the boot details on the drive
Legacy matches the MBR format your Kali install must be on. It just looks for the 1st partition on drive to boot operating system
I think you can add the kali install to the win 10 boot menu so it knows it exists.
How would i be able to add the kali linux option to the boot menu?