You can try this tuto_by_sysmatck_ubuntuforums.org
First Step: Format USB drive
To create a EFI firmware compatible boot drive, you need a GPT partition table and at least one FAT32 partition. Do as follows...
sudo apt-get install gdisk
sudo sgdisk --zap-all /dev/sdb
You probably need to remove and insert the USB drive again at this point for the kernel to update information about it...
sudo sgdisk --new=1:0:0 --typecode=1:ef00 /dev/sdb
sudo mkfs.vfat -F32 -n GRUB2EFI /dev/sdb1
Second Step: Copy files and Set directory structure
Let's mount the usb drive
sudo mount -t vfat /dev/sdb1 /mnt -o uid=1000,gid=1000,umask=022
To make life easier, I created a pack with all necessary files for you to modify as you need usb-pack_efi. If you don't trust my files, create yours using this page as reference.
Extract the zip file and paste those inner files using Command Line Interface or a file manager you like.
rsync -auv usb-pack_efi/ /mnt
The most important files are bootia32.efi to boot on 32bit machines, bootx64.efi to boot on 64bit machines and grub.cfg to setup grub to load ISOs or chainload to other paths.
In the end, you might get a directory tree like this:
Third Step: Install GRUB2 on the drive
sudo grub-install --removable --boot-directory=/mnt/boot --efi-directory=/mnt/EFI/BOOT /dev/sdb
Fourth Step: Setup ISOs to be loaded
Put (copy) the .iso files you want to load in
/mnt/iso/ and setup
grub.cfg like the existing examples...
Note that the most important variable to set is isofile. There is lots of examples on the web about how to configure grub2 menu. Use
# to comment those lines you don't want to use, e.g. to hide a configuration of absent .iso at /iso.
Last Step: Configure firmware and Test
First and most important, deactivate secure boot on your computer's firmware. Search on the web if you don't know how.
To boot the USB drive you can set your machine firmware to search first for the USB device (boot order). Or you can choose what drive to boot as soon as you turn on your computer. Each manufacturer has its own keys to do it. Search for your machine's manual if needed.
thank you sysmatck