The button and no link routes and attributes are not retrieved from the url object in the menu_footer pattern.

I have rebased the MR.

I am not very comfortable with this part:

        {% set is_button = item.url == 'route:<button>' ? true : false %}
        {% set is_plain_text = item.url == 'route:<nolink>' ? true : false %}

First, because we may not need the ternary:

        {% set is_button = (item.url == 'route:<button>') %}
        {% set is_plain_text = (item.url == 'route:<nolink>')  %}

Second, and that's the most important, I would prefer to not manipulate route information from the template.

UI Patterns Settings 2.2 & 2.3 were released last week with some improvement in the menu processing: https://www.drupal.org/project/ui_patterns_settings/releases/8.x-2.3 →
Is it helping?