qemu-img can convert many formats.
Here is an example of how to convert different images to different formats for QEMU-KVM
The example above converts a raw windows2019.img file from QEMU to a Virtualbox .vdi
qemu-img convert -f raw -Ovdi windows2019.img windows2019.vdi
-f raw = this means the format of the source image (instead of raw it could be vdi, vmdi, qcow2 etc..)........
In short the solution is just to use vgremove for the actual /dev/mapper device:
vgremove /dev/mapper/backups-backuplv
box mnt # mdadm --manage /dev/md8 --stop
mdadm: Cannot get exclusive access to /dev/md8:Perhaps a running process, mounted filesystem or active volume group?
box mnt # lv
lvchange lvconvert lvcreate l........