I've finally selected my new Linux live multiboot manager: "Ventoy is an open source tool to create bootable USB drive for ISO/WIM/IMG/VHD(x)/EFI files. With ventoy, you don't need to format the disk over and over, you just need to copy the ISO/WIM/IMG/VHD(x)/EFI files to the USB drive and boot them directly. You can copy many files at a time and ventoy will give you a boot menu to select them." Very easy to use and 100% open source: