For me… I have a symbolic link for a “Games” folder that points to another physical hard drive… this was where I was initially trying to specify where to install… and the default for saved games which is “$HOME/Documents” is also a symbolic link in my case…
What I did out of curiosity was removed my sym links… attempted the install script again and just left every default ( Next… Next… etc ) … it worked fine… so I then moved everything, recreated my links and moved the prefix etc to where I wanted it… manually.
I didn’t spend any further time investigating it… I finally had a working prefix.
But ( For me ) there definitely seems to be an issue if the landing points are not the same device and/or sym links … in my case they where both… so not sure if its just sym link resolving or just an issue with being a separate /dev/sd? endpoint.