Yes, it is possible to do although it is not easy as it is completely not documented here. So you need to have a lot of free time and patience! ))
I think the easiest way is to make Extlinux extended menu with separate kernels, initrd and dtb files of different distros each in separate folders on fat 16/32 Boot partition and corresponding RootFS-s on separate ext4 partitions. See syslinux.org for details. But I couldn’t make a graphical menu work. You can also try installing ReFind with the same configuration to use multiboot GUI but it is more difficult to do.
Then you can also try installing Grub for EFI arm64 to use multiboot GUI but it also requires a lot of manual steps and reading manuals. You need to make your NVME drive GPT partitioned with a small FAT16/32 EFI system 1st partition. And you also need to have a generic or generic-efi image of distro you’d like to use and manually copy vim4 DTB file into Boot directory. And if it works and the distro is booting up then you can try installing Grub. You can split your NVME drive into several Ext4 partitions following EFI partition (Nvme0n1p1) and try installing Manjario generic-efi image for example on Nvme0n1p2 partition and Armbian generic image on Nvme0n1p3. And if it works then sudo update-grub should recognize all distros on your drive and add them to grub,cfg and multiboot menu.
But you also need to check if your keyboard works at initial stage of uboot loading because many of the models don’t because their drivers are not supported in Uboot. You should press any button as soon as the booting process starts and then press space at the init sequence prompt: “Hit SPACE in 2 seconds to stop autoboot”. If it works then you can enter uboot or kbi menu (write help to have a list of available commands) and you can use your keyboard later for switching among multiboot menu items. It seems that Logitech USB keyboards work.
To start the experiments you can try Online boot scripts in OOWOW to install Ubuntu generic image on NVME drive if it is available for Vim4. Or download Manjaro generic-efi image from their github and burn it to NVME drive with Balena etcher. Then don’t forget to copy Vim4 DTB file into Boot directory and if it starts using extlinux.conf you will need adding or changing the line like this into this file:
FDT /boot/dtb-5.19.16-meson64 (your DTB folder name) /amlogic/ Your board meson khadas-vim4.dtb
You also need to have a mainline uboot in EMMC or SPI as it supports booting from NVME
Thanks a lot for this post, sorry for the late reply. I need some time to properly process this and probably quite awhile for experimentation and then I think I have a decent chance of getting this to work. I know pretty well how to run multiple OS on my PC, but I will have to read up on U-BOOT and DTB since I know next to nothing about those. If it is possible a multiboot like refind would be very nice if I could get that to boot from emmc and then select a OS on the SSD and having the efi partition on the emmc.
You have given me a good guideline on how to get this to work and I sincirely thank you for your post.