Create a button with new news post linked to templates

THOREX Use link in below format to create a new news post: 

https://contoso.sharepoint.com/sites/siteName/_layouts/15/CreatePageFromTemplate.aspx?source=/sites/siteName/&promotedState=1

Also, you can hide New option in site pages library using JSON view formatting: 

{
  "commandBarProps": {
    "commands": [
      {
        "key": "new",
        "hide": true
      }
    ]
  }
}

Output: 

Documentation: Command bar customization syntax reference 

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