I’'d second skypilots advice, but to be safe, do you have two NVME slots on your motherboard?? If you do you can put the new drive into thast empty slot. do a complete clone of the drive which will ensure it becomes bootable, then you’ll have your free space and the old drive to reformat and use as you wish.
You will need to get into your BIOS in order to change the boot drive that you wish to use.