Problems with linux vdisks

[Midas]

I have been trying to follow the setup detailed in https://www.ventoy.net/en/plugin_vtoyboot.html, but I always get stuck with the same errors.





I've been mostly trying this to setup 'linuxmint-20-mate-64bit.iso' and have tried booting the vdi.toy created with VirtualBox in Ventoy v1.0.41, v1.0.32, etc.

I have working VHDs with Windows in the same locations that boot alright before that -- i.e., when I get such errors, nothing boots anymore and I have to reboot.

What am I doing wrong?