Linux on External SSD issues Reboot and select proper boot device, how to fix it?

Question

linux

Hello, I have a problem running Debian on an external M.2 (USB 3.1 Gen 2) 120GB Transcend SSD. The system was installed in a virtual machine, the GRUB system bootloader was successfully installed.
In VirtualBox, the axis works, but when I start the Asus ROG GL502VS laptop via an external SSD in UEFI, a black screen appears and the message Reboot and select proper boot device appears. Please tell me how to fix this problem?

Answer 1

1) We need to find out who issues this message - BIOS / UEFI, GRUB, Linux OS Loader or the Linux startup system (kernel and subsequent scripts). What were the messages before?
2) Maybe UEFI didn't like Linux. It is necessary to disable "secure boot", in which UEFI checks the digital signature.
3) I did not understand how the system worked inside the virtual machine. Was it directly loaded from an external drive? Or was an image used, which was then transferred to an external drive?
4) I have strong suspicions that inside the virtual machine and on the physical external drive there is a difference in device naming. At least, in FreeBSD this is exactly the case: the internal disk (and the disk image inside the virtual machine) is called /dev/ad*; to a flash drive - as SCSI: /dev/da*. Although with this option - there would be a message like "I can not mount the file system", i.e. would be the word "mount".
This problem is solved in FreeBSD by using GEOM marks, which are written to the disk or partition and are independent of the connection method.
Write about the results, I'm also interested.