Ich habe es geschafft, diese 100 GB durch einen vierstufigen Prozess wiederherzustellen
Mounted a new Disk (/dev/sdc) with same size as incompletely used disk (/dev/sda4) and used pvcreate and lvextend to add it as a logical volume to the LVM volume group I used pvmove to move the data from /dev/sda4 . This took ~16 hrs but was seamless. It automagically moved it to new /dev/sdc volume and then showed that /dev/sda4 was unused. I pvremoved the /dev/sda4 from the volume group I used fdisk to remove the existing partition and repartitioned the space using gparted. I added this volume to the volume group( pvcrate and lvextend) and then was able to use up all size with a sudo lvresize -r -l +100%FREE /dev/ubuntu-vg/root This added back that 100GB which was not incorporated into the partition and also the volume-group.