Role authors, don't do this in your role

nope.yaml

# If you specify a variable for users to set outside your role
# DO NOT overwrite it later.
#
# Due to precedence rules the combined value here will
# never be set in some cases, e.g when using include_role
#

- name: Set netbox_config.SECRET_KEY to generated SECRET_KEY
  set_fact:
    netbox_config: "{{ netbox_config | combine({'SECRET_KEY': _netbox_secret_key_file['content'] | b64decode}) }}"

# Instead, use an "internal variable" if you need to do combines or similar

- name: Set netbox_config.SECRET_KEY to generated SECRET_KEY
  set_fact:
    _netbox_config: "{{ netbox_config | combine({'SECRET_KEY': _netbox_secret_key_file['content'] | b64decode}) }}"

# Use the internal fact from this point ...
# Pretty? No. Does it work? Yes.