Is it possible to loop through array of specific host and configuration

I'm trying to figure out if it's possible to have a play that will loop through an array of hosts with a specific host variable configured/defined.

For example, this is my inventory file

controlplanes:
  hosts:
    host1.example.com:
workers:
  hosts:
    host2.example.com:
      longhorn:
        storage: true
    host3.example.com:
      longhorn:
        storage: true

Basically my goal is to run kubectl label command from one host to apply annotations to specific kubernetes nodes, but I only want to have the command run against a specific list of hosts, e.g. hosts that have longhorn.storage=true, so in the above example, I should only loop through 2 hosts.

Is this possible? I know I can loop through all hosts, but I can't seem to access variables of any given host, I thought hostvars[hostname].longhorn.storage might give me access, but results seem to indicate it's not defined, so I think my approach is incorrect.

- name: Loop Test
  hosts: controlplanes
  tasks:
    - debug:
        msg: "{{ item }}"
      loop:
        - "{{ groups['all'] }}"

Solution

Create the list longhorn_group in the first play

- hosts: all
  tasks:
    - set_fact:
        longhorn_storage: "{{ longhorn.storage|d(false) }}"
    - set_fact:
        longhorn_group: "{{ hostvars|dict2items|
                            selectattr('value.longhorn_storage')|
                            map(attribute='key') }}"
      run_once: true

and use it in the second play

- hosts: controlplanes
  tasks:
    - debug:
        var: longhorn_group
    - debug:
        msg: "{{ item }}"
      loop: "{{ longhorn_group }}"

gives (abridge)

^{TASK [debug] *********************************************************************************
ok: [host1.example.com] =>
longhorn_group:
- host2.example.com
- host3.example.com

TASK [debug] *********************************************************************************
ok: [host1.example.com] => (item=host2.example.com) =>
msg: host2.example.com
ok: [host1.example.com] => (item=host3.example.com) =>
msg: host3.example.com}

^{Example of a complete playbook for testing
- hosts: all
tasks:
- set_fact:
longhorn_storage: "{{ longhorn.storage|d(false) }}"
- set_fact:
longhorn_group: "{{ hostvars|dict2items|
selectattr('value.longhorn_storage')|
map(attribute='key') }}"
run_once: true

- hosts: controlplanes
tasks:
- debug:
var: longhorn_group
- debug:
msg: "{{ item }}"
loop: "{{ longhorn_group }}"}