This problem has two solutions as given below:

I made an alternative solution for this:

• I check in the database. The new page is in the cms_page table but the link with cms_page_store. How to solve this?
  • Disable single store mode (Admin > Stores > Configuration > General > General > Single-Store Mode) and select “No”.
  • Assign a store view to the CMS page.
  • Go to your cms pages ( Admin > Content > Pages)
  • Edit the page which gives you the 404 message
  • Set the store view to “Default Store Views”
  • Save the page
  • Refresh cache (Admin > System > Cache Management) Now the CMS page is saved to table “cms_page_store”. and pages are working.
• And, the second solution works on while Single Store Mode is Enabled.
  • Go to Content > Pages
  • Click on the page which is not working or spitting 404
  • Two-button save and cancel appears
  • Click on save
  • Check your page on frontend
  • This will start working