I’ve never installed fedora specifically but…

Anyway I created a free 900GB ext4 partition

It’s either ext4 or free, can’t be both. Now, if it was ext4, Fedora would for sure detect it as such, so I’m not sure what it is.

I assume you would want to click on sda6 in the installer, then the “-” button to delete whatever is there, and then it would recognize it as available space.

Check my other comment. sda6 is there.

sda6 is the fourth one (after sda3) in the list on the bottom picture. The partitions seem to be physically in that order, but labeled differently, as they were created. You can reorder the labels but it’s also fine left alone AFAIK.

Any self-respecting distro pushed an update to fix this days ago, so just updating (and restarting cups) will do. But if you don’t print anyway, you might as well disable it.