WSL: If your friend is a dev and needs Linux cli utilities, use this. Dual Boot: If your friend wants to daily drive Linux, use this. Shrink Windows NTFS partition within Windows then install Linux to blank space. Virtualbox: Testing ground for dual boot, your friend can familiarise themselves with Linux safely using a VM.
You gotta br kidding me. These people have no idea what kind of disservice they do to Linux.