Considering the following test playbook:

---
- name: Playbook
  hosts: localhost
  become: false
  gather_facts: false
  vars:
    first:
      alpha: 1
      gamma: 3
    second:
      beta: 2
  tasks:
    - name: Import facts
      ansible.builtin.import_role:
        name: helm
        tasks_from: facts

    - name: Debug
      ansible.builtin.debug:
        msg: "{{ lookup('ansible.builtin.dict', first | combine(second)) }}"

Which produces the expected key, value result:

ok: [localhost] =>
  msg:
  - key: alpha
    value: 1
  - key: gamma
    value: 3
  - key: beta
    value: 2

While applying the dictsort filter (documentation):

msg: "{{ lookup('ansible.builtin.dict', first | combine(second) | dictsort) }}"

The following error is produced:

fatal: [localhost]: FAILED! =>
  msg: 'An unhandled exception occurred while running the lookup plugin ''ansible.builtin.dict''. Error was a <class ''ansible.errors.AnsibleError''>, original message: with_dict expects a dict. with_dict expects a dict'

I was wondering what is the proper dictsort usage, thank you for your input.