I have been using USB Image Tool to create backups of my installations and then using balenaEtcher to restore them. I have not used Win32DiskImager, but I think it should work. I’m not familiar with Pishrink either, but I used an 8GB eMMC to create the image, then when I flashed it into my 64GB eMMC I was able to add the unallocated space using Disks on Ubuntu.
I think USB Image Tool, should be a good option to backup your Ubuntu Installation.