ui_icons-1.0.x-dev/modules/ui_icons_picker/ui_icons_picker.routing.yml

ui_icons_picker.ui:
  path: '/ui-icons/ajax/picker-icon-library'
  defaults:
    _form: 'Drupal\ui_icons_picker\Form\IconSelectForm'
  requirements:
    _permission: 'access content'
    _method: 'POST'