andrejr [1] filed a deletion request for multibootusb-git [2]: The software has been abandoned by the maintainers (https://github.com/mbusb/multibootusb) and deprecated in favor of Ventoy (https://github.com/ventoy/Ventoy).
The build presented in the package is nowadays pretty broken and doesn't work for most new distro releases. Nobody should be using it. [1] https://aur.archlinux.org/account/andrejr/ [2] https://aur.archlinux.org/pkgbase/multibootusb-git/
