unable to boot from disk

[husky]

Hi!
I recently found that the modem port inside my Lenovo T14 AMD can be used to host an NVMe drive, too, and decided to use it as an emergency drive containing several ISOs and the like in order to rescue anything if necessary - sysrescd, kali, ubuntu, ...

So I got me Ventoy 1.0.35 and unpacked the tar on my Linuxmint OS, fired up a terminal and ran 

Code:

sudo ./Ventoy2disk.sh -i -s -g /dev/nvme1n1

Then I enrolled the necessary key using 

Code:

sudo mokutil --import ENROLL_THIS_KEY_IN_MOKMANAGER.cer

and copied some ISOs to the Ventoy partition. Then I rebooted in order to verify the enrollment. After completing it I rebooted and opened the boot device list. My Linuxmint drive was listed as 'ubuntu' and started up like before, but the Ventoy disk was displayed only with its manufacturer and model. Nevertheless I selected it and tried to boot into ventoy - but to no avail.

Since I ended up with Grub 2.02 command line (and my Linuxmint uses Grub 2.04) I think I was in the correct location.
I tried to load the Grub config, but this only resulted in an error

Code:

error: cannot find command vt_list_img

being displayed and then a strangely looking grub menu came up, telling me that no ISO could be found.

Obviously something is wrong - but I'm a bit lost for now.

Any hint anyone?