Hi Por_85,
I am Dave, I will help you with this.
In your screenshot, you have run the List Disk command, but you are missing the Select Disk command before running the Clean and so the command does not know what disk you want to work on, and convert gpt commands, please try these steps.
To convert your Drive to GPT:
At the very start of the Installation Process, press Shift + F10, or Shift + Fn + F10 to open Command Prompt
Run this command and hit Enter:
diskpart
Run this command and hit Enter:
list disk
(Make note of the disk number you want to convert and enter it into the next command - replace X)
Run this command and hit Enter:
select disk X
Run this command and hit Enter:
clean
Run this command and hit Enter:
convert gpt
Then close Command Prompt