@Thomas_G Hallo! Thanks for your help.
I checked the existence of the pages.
Topic.with_deleted.exists?(SiteSetting.guidelines_topic_id)
Topic.with_deleted.exists?(SiteSetting.tos_topic_id)
Topic.with_deleted.exists?(SiteSetting.privacy_topic_id)
The results are all true so I tried to recover.
faq = Topic.with_deleted.find(SiteSetting.guidelines_topic_id)
tos = Topic.with_deleted.find(SiteSetting.tos_topic_id)
pp = Topic.with_deleted.find(SiteSetting.privacy_topic_id)
faq.recover!
tos.recover!
pp.recover!
The recover succeeded on terminal but /faq, /toc and /privacy showed error.
Then I checked topic_id of those topics from terminal and set urls to /admin/site_settings/category/legal.
Now the pages are fine. Thank you!