charasheet/src/character/templates/character/snippets/character_details/gm_notes_update.html

<div class="mt-3" id="gm-notes">
    <form>
        <h2>
            Notes MJ
            <a hx-post="{% url "character:gm_notes_change" pk=character.pk %}"
               hx-target="#gm-notes"
               hx-swap="innerHTML"
               class="btn btn-primary btn-sm"
            >
                <i class="fa-solid fa-save"></i> Save
            </a>
        </h2>
        <div class="alert alert-info">Ces notes ne sont pas visibles par le joueur.</div>
        {% csrf_token %}
        <textarea class="form-control" name="gm_notes" rows="10">{{ character.gm_notes }}</textarea>
    </form>
</div>