I found two settings which, although available in the Settings admin panel and in site_settings.yml, seem to be missing in app.SiteSettings
:
export default {
name: 'my-plugin',
initialize(container, app) {
console.log(app.SiteSettings.tagging_enabled) // => true
console.log(app.SiteSettings.max_tag_length) // => 20
console.log(app.SiteSettings.allow_duplicate_topic_titles) // => undefined
console.log(app.SiteSettings.min_trust_to_create_tag) // => undefined
}
}