@fredx181 and other members desiring a Ventoy-SG2D setup EXAMPLE on a system drive instead of a USB.
For some reason, it appears that a prior post for you has been lost on the forum. Hopefully, this post wont get lost.
No USB used on this PC to boot ISO files as well as installed OSes.
Anyway, here's pics on the 2 system drive test PC I have. Its 2nd drive is the main bootable drive of the system out of power-on (POST). It is a Ventoy drive. Hopefully the following is helpful understanding. It is a flawless example in my use. Download ISO files, boot them, and saving forum distro persistence for ALL.