If you plan to install an OS that does not support GPT disks, conversion of the GPT disk to MBR is possible the name of the operation will be listed as Convert to MBR.
If you need to convert a GPT disk to MBR:
You will receive a warning window, stating that you are about to convert GPT into MBR.
You will be explained the changes that will happen to the system after the chosen disk is converted from GPT to MBR. E.g. if such conversion will stop a disk from being accessed by the system, the operating system will stop loading after such conversion or some volumes on the selected GPT disk will not be accessible with MBR (e.g. volumes located more than 2 TB from the beginning of the disk) you will be warned here about such damage.
Please note, a volume, belonging to a GPT disk to convert, will be a logical one after the operation and is irreversible.
(To finish the added operation you will have to commit it. Exiting the program without committing the pending operations will effectively cancel them.)