For ages, there have been Zalman enclosures for making ISO-based multi-bootable external HDDs/SSDs working this way and on a lower level. And iodd which are ess

For ages, there have been Zalman enclosures for making ISO-based multi-bootable external HDDs/SSDs working this way and on a lower level. And iodd which are essentially the same (AFAIK Zalman rebranded them).