What is the best way to install on 5tb portable storage?

[Algernon]

I have a mypassport plug and play storage that appears as sdb. I could not install ventoy regularly to it with the exe even by running with the extra parameter letter, it still does not appear as an option, this only showed my internal drive extra. I first cloned a normal ventoy usb to it with easeus(I imagine copying would be the same but to be safe), then after tried to install on linux, this gave me an error mnt folder already existed but it says it installed successfully. I can boot in uefi on my true pc using either method but bios usb boot greets me with "GR.. then a no boot grub screen on both vb and real machine. 
    In virtualbox I am getting stuck at the uefi shell when booting with efi (have created usb.vmdk, ran as admin), it does not appear to find the fs0 or default efi mapping just blk device. Is there any trick for this, would secureboot or non-secure be recommended here? What is the maximum size drive for mbr support? The drive is empty now, is there anyway to make it appear as less space to allow dual legacy mbr bios & gpt boot, or just to ventoy boot the 5tb drive from uefi in virtualbox?All works ok with a 64gb usb. I would like to dedicate around 250gb to ventoy or maximum mbr allows if possible and collect iso and store them on it as time goes by. My apologies for so many questions, any help much appreciated.

[longpanda]

1. Your drive is 5TB, so you can only use GPT partition style NOT MBR
2. Some legacy BIOS machine can boot the GPT style Ventoy drive, but some can NOT
3. In Linux, before install Ventoy, run mount  command to see whether  /dev/sdb1 /dev/sdb2 ... has been already mounted, if so umount them.
4. In Linux, you just run  sh Ventoy2Disk.sh -I -g /dev/sdb to install Ventoy