I installed Debian 10, using the boot disk to encrypt the entire disk, and create a logical volume manager. Now I would like to install a completely separate instance of Debian. However, when I install GParted on a Debian 10 boot disk, GParted can not successfully make any changes. I had a friend who's rather experienced with Linux play around with it for two hours, and he concluded that the logical volume manager is to blame. He recommended I use system-config-lvm, but unfortunately Debian 10 is not supported. So I burnt a live DVD of Debian 9.12 (Stretch), ran system-config-lvm, and got the error "Unsupported LUKS version 2." I then tried to update lvm and was told it was running at the most recent version.
How can I add a partition (for a separate operating system) to this disk? Any utilities (or other distro's live DVD) I should try? Or do I just have to wipe the whole disk clean and start over?
*Per user "Emmanuel Rosa", here is the output of when I run lsblk on the Debian 10 live DVD:
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT loop0 7:0 0 2G 1 loop /usr/lib/live/mount/rootfs/filesystem.squashfs sda 8:0 0 119.2G 0 disk ├─sda1 8:1 0 243M 0 part ├─sda2 8:2 0 1K 0 part └─sda5 8:5 0 119G 0 part sr0 11:0 1 2.2G 0 rom /run/live/medium