Cos there's two different issues in one, I can't properly follow the format in the guidelines :/
Issue 1: Installer progression goes as follows:
Set OS language
Set keyboard language
Connect to wifi?
You need at least 15.5gb of disk space to install, your computer has 0.0 B of space free
Issue 2: Seemingly unable to select install destination
I did ask a friend in another discord server for some help with this, and apparently Issue 2 is cos it's somehow not detecting the intended installation drive. (Garuda found it without issues so why it won't find it now beats me lol)
Attached is a run through of the Installer from launch to problem page.
Note: in the "Disks" program it shows the drive in question, and even let's me mount and unmount it, but the Installer seems unable to find it from the bootable USB.