Download https://www.memtest86.com/downloads/memtest86-usb.zip

unzip it.


see (thx krish!!)  https://www.yosoygames.com.ar/wp/2020/03/installing-memtest86-on-uefi-grub2-ubuntu/
(https://www.linuxquestions.org/questions/linux-general-1/how-to-mount-img-file-882386/ ## old)


Get your memtest86-usb.img online as loop device like:

    mount -o loop,offset=263192576 /home/hackbyte/opt/memtest/memtest86-usb.img /mnt/memtest/

copy over everything from:

sol|root|20:49:46|~| 0# ls -la /mnt/memtest/EFI/BOOT/
total 4684
drwxr-xr-x 3 root root    4096 May  7 23:38 .
drwxr-xr-x 3 root root    4096 May  7 23:38 ..
-rwxr-xr-x 1 root root 1144864 May  7 23:38 BOOTIA32.efi
-rwxr-xr-x 1 root root 1260640 May  7 23:38 BOOTX64.efi
drwxr-xr-x 2 root root    4096 May  7 23:38 Benchmark
-rwxr-xr-x 1 root root    4181 May  7 23:38 blacklist.cfg
-rwxr-xr-x 1 root root    6823 May  7 23:38 mt86.png
-rwxr-xr-x 1 root root 2358510 May  7 23:38 unifont.bin


to your /boot/EFI/memtest dir


afterwards you need to add your memtest to your (U)EFI boot menu using efibootmgr like this:

efibootmgr -c -d /dev/sda -p 1 -L "memtest"  -l "\EFI\memtest\BOOTX64.efi"