open core for Sonoma with 2017 iMac Fusion Drive

hi guys,

For the post install, it's letting me choose either the ssd or the hd, like it doesn't understand it's a Fusion Drive. I'm a bit afraid to just pick one because I already had to do a clean install as it broke the Fusion Drive on my first go around.

I looked through the forums but can't find a clear answer - what's the best way to set this up so I don't need the external usb anymore? do I just pick the SSD option, simple as that? do I install it on both? something else I haven't even imagined yet??

thanks!