Considering the following test playbook:

---
- name: Node Tolerations
  hosts: localhost
  gather_facts: false
  vars:
    tolerations:
      - key: node.cilium.io/agent-not-ready
        operator: Exists
        effect: NoExecute
      - key: node-role.kubernetes.io/control-plane
        operator: Exists
        effect: NoSchedule
  tasks:
    - name: Set node taints fact
      ansible.builtin.set_fact:
        node_taints: "{{ (node_taints | default([]) | union([':'.join((item.key, item.effect))])) }}"
      with_items: '{{ tolerations }}'

    - name: Set node toleration fact
      ansible.builtin.set_fact:
        node_toleration: "{{ node_taints | select('search', 'control-plane') }}"

    - name: Variable output
      ansible.builtin.debug:
        var: node_toleration

Which produces the expected result:

ok: [localhost] =>
  node_toleration:
  - node-role.kubernetes.io/control-plane:NoSchedule

While using the node_toleration fact into a Jinja2 template:

node-taint:
  {{ node_toleration | indent(2) }}

The following error is generated:

AttributeError: 'list' object has no attribute 'splitlines'

As temporary workaround, I used:

node-taint:
  - {{ node_toleration | join }}

But I prefer the initial Jinja2 format, allowing me to define the proper indentation. I was wondering if you can provide some insight, what would be the proper fix.