Freespace becomes Unusable when partitioning disk for Ubuntu Installation

Solution 1:

You've clicked the "free space' and hit the little "+" button, to add a partition there, yes? DO NOT click "New Partition Table", that will torch your entire system, you don't want that - instead, click the "free space" line, and then use that little "+" to create your partition.

If your disk is an MBR it'll tell you that you can't use the space because you can only have 4 primary partitions, or that option will be greyed out. That's a limitation of MBR, and if your Windows is old enough then it defaulted to MBR.

If the disk is NOT an MBR partition table format, then the icon and button should work and it should then ask you to create a partition there. Mount point will be / and your filesystem type should be ext4 for it to work properly for Ubuntu. Then it should install there.