I use Mac mini with virtual box 7.0 to install
If I were to guess… something went wrong with Virtual Box reading the .ISO for installing.
If I were to guess further, your Mac Mini has an ARM chip and you’re emulating x86. Or perhaps not emulating x86, and there are still issues with Virtual Box on ARM.
If you are using an ARM chip, trying following our UTM guide and use UTM instead of Virtual Box. (Running StartOS on Mac M1/M2)
My mac mini has a intel chip
Then I’d try downloading the correct ISO again, and tinkering with VirtualBox’s settings related to emulating a bootable USB. The issue is somewhere around there.