virtualbox.org

I think I understand that it is not possible to change the size at the Guest PC disk drive after its installation.
The size can only be determined before installing the ISO file.
It's correct?
Is there a possible solution using to this?
What can I do on the Storage tab?

No, that is not correct. Drive capacity can be changed in File|Virtual Media Manager.

How to resize a Virtual Drive.

The procedure is slightly different:
01 - From the Menu called Oracle VM VirtualBox Manager, click on File, Virtual Media Manager
02 - In the opened window called Virtual media manager, the Guest PCs are listed;
03 - Select the Guest PC to modify and move the blue cursor to change the size of the disk drive;
04 - Click on Apply.
With VirtualBox version 6.1.32 it is only possible to increase the size, it is not possible to decrease the size.

Thank you.

Slightly different from what? Your list is taken from the FAQ, except you get the terminology wrong: you are resizing drives, not PCs. There is no 1:1 correspondence between PCs and drives.

I did not take this procedure from the faq, I wrote it while I was running the commands and modestly I thought it could be useful to other users of the forum.
Regarding the terminology, you are right that I am resizing the disk drive, but it is VirtualBox that calls the disk drives using the name I assigned to the Guest PC.
I don't want to make controversy.

ermete74 wrote:it is VirtualBox that calls the disk drives using the name I assigned to the Guest PC.

That behavior is the default, true, but you can override the behavior and name the disk file anything allowed by the host file system.

The disk files listed in the Virtual Media Manager are not the VMs, only the disk files.