Not sure if it's something on my side, but I cannot see to access a subsection of the volume commands from the CLI client.

openstack volume backend pool list
openstack: 'volume backend pool list' is not an openstack command. See 'openstack --help'.
Did you mean one of these?
  volume attachment complete
  volume attachment create
  volume attachment delete
  volume attachment list
  volume attachment set
  volume attachment show
  volume backup create
  volume backup delete
  volume backup list

/usr/local/lib/python3.9/site-packages/openstack/

drwxr-xr-x   41 laurentdumont  admin   1.3K  2 Jun 17:03 .
drwxr-xr-x  187 laurentdumont  admin   5.8K 20 Sep 09:47 ..
-rw-r--r--    1 laurentdumont  admin   2.4K  2 Jun 17:03 __init__.py
-rw-r--r--    1 laurentdumont  admin   1.2K  2 Jun 17:03 __main__.py
drwxr-xr-x   15 laurentdumont  admin   480B  2 Jun 17:03 __pycache__
-rw-r--r--    1 laurentdumont  admin   1.4K  2 Jun 17:03 _hacking.py
-rw-r--r--    1 laurentdumont  admin   4.6K  2 Jun 17:03 _log.py
-rw-r--r--    1 laurentdumont  admin   5.6K  2 Jun 17:03 _services_mixin.py
drwxr-xr-x    7 laurentdumont  admin   224B  2 Jun 17:03 accelerator
drwxr-xr-x    8 laurentdumont  admin   256B  2 Jun 17:03 baremetal
drwxr-xr-x    6 laurentdumont  admin   192B  2 Jun 17:03 baremetal_introspection
drwxr-xr-x    8 laurentdumont  admin   256B  2 Jun 17:03 block_storage
drwxr-xr-x   28 laurentdumont  admin   896B  2 Jun 17:03 cloud
drwxr-xr-x    7 laurentdumont  admin   224B  2 Jun 17:03 clustering
drwxr-xr-x    7 laurentdumont  admin   224B  2 Jun 17:03 compute
drwxr-xr-x   14 laurentdumont  admin   448B  2 Jun 17:03 config
-rw-r--r--    1 laurentdumont  admin    21K  2 Jun 17:03 connection.py
drwxr-xr-x    6 laurentdumont  admin   192B  2 Jun 17:03 database
drwxr-xr-x    6 laurentdumont  admin   192B  2 Jun 17:03 dns
-rw-r--r--    1 laurentdumont  admin   8.6K  2 Jun 17:03 exceptions.py
drwxr-xr-x    5 laurentdumont  admin   160B  2 Jun 17:03 fixture
-rw-r--r--    1 laurentdumont  admin   1.6K  2 Jun 17:03 format.py
drwxr-xr-x    8 laurentdumont  admin   256B  2 Jun 17:03 identity
drwxr-xr-x   11 laurentdumont  admin   352B  2 Jun 17:03 image
drwxr-xr-x    6 laurentdumont  admin   192B  2 Jun 17:03 instance_ha
drwxr-xr-x    6 laurentdumont  admin   192B  2 Jun 17:03 key_manager
drwxr-xr-x    7 laurentdumont  admin   224B  2 Jun 17:03 load_balancer
drwxr-xr-x    7 laurentdumont  admin   224B  2 Jun 17:03 message
drwxr-xr-x    7 laurentdumont  admin   224B  2 Jun 17:03 network
drwxr-xr-x    6 laurentdumont  admin   192B  2 Jun 17:03 object_store
drwxr-xr-x    8 laurentdumont  admin   256B  2 Jun 17:03 orchestration
drwxr-xr-x    6 laurentdumont  admin   192B  2 Jun 17:03 placement
-rw-r--r--    1 laurentdumont  admin    29K  2 Jun 17:03 proxy.py
-rw-r--r--    1 laurentdumont  admin     0B  2 Jun 17:03 py.typed
-rw-r--r--    1 laurentdumont  admin    88K  2 Jun 17:03 resource.py
-rw-r--r--    1 laurentdumont  admin    13K  2 Jun 17:03 service_description.py
drwxr-xr-x    6 laurentdumont  admin   192B  2 Jun 17:03 shared_file_system
drwxr-xr-x    9 laurentdumont  admin   288B  2 Jun 17:03 tests
-rw-r--r--    1 laurentdumont  admin    12K  2 Jun 17:03 utils.py
-rw-r--r--    1 laurentdumont  admin   641B  2 Jun 17:03 version.py
drwxr-xr-x    7 laurentdumont  admin   224B  2 Jun 17:03 workflow
 usr/local/…/site-packages/openstack
 %  python3
Python 3.9.2 (default, Mar 26 2021, 23:27:12)
[Clang 12.0.0 (clang-1200.0.32.29)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>