How to reliably know disk name if one of its partition's name is known

Question

I am working on a linux bash script that takes a disk partition name as user input. It then needs to check if the drive is using GPT or not, for which I use the following if statement:

# Must be run as root
if [[ $(fdisk -l $DISKNAME | grep -i 'Disklabel type') = "Disklabel type: gpt" ]]; then
  echo "Yes, its GPT"
fi

The variable DISKNAME has to store the name of the disk drive and not the partition. I could just remove the number at the end of the partition name but that is not consistent with SSDs and NVMes. For example NVMe disk name can be /dev/nvme0 and drive name can be /dev/nvme0p1.

I am searching for a reliable way (not string manipulation) to know the drive name when a partition name is already known.

EDIT: I could also ask the user for the drive name but then there is space for user errors.