failed to open a page on safari

Go step by step and test.

1. Update Safari, if an update is available. Update may come with bug fixes.

    Update to the latest version of Safari - Apple Support

    Update macOS on Mac - Apple Support

2. Force Quit Safari, launch Safari holding the Shift key down.

    https://support.apple.com/en-us/HT203987

3. Startup in Safe Mode. 

   https://support.apple.com/guide/mac-help/start-up-your-mac-in-safe-mode-mh21245/mac.  

    Quote:

    It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. 

    And it deletes some system caches, including font caches and 

    the kernel cache, which are automatically created again as needed.

4. Clear History

    Clear your browsing history in Safari on Mac - Apple Support

    Please read the article before clearing history, 

    this is like a low level resetting of Safari without affecting passwords and bookmarks.

5. If Safari doesn't open a webpage or isn’t working as expected

    https://support.apple.com/en-us/HT204098

6 Upgrade mocOS

How to get old versions of macOS - Apple Support