I recently submitted to the Ventoy path, can't believe it took me so long.
I actually thought I had messed something up after burning it on a USB. The drive mounted an empty folder and I thought, "no way it's that simple, I don't just drop the ISOs into the folder do I?"
Yes, you just throw all your ISOs into that folder, unmount, and you're good to go!
Meanwhile I mount the ISO, copy paste its contents to a ~150 GiB FAT32 partition on my HDD I used for backing up PS3 and then modify grub.cfg so GRUB can pass the correct arguments to Linux kernel.