Search Engine Default Issues in Safari

 1. Check for adware.

     Run the latest release of Malwarebytes for Mac to remove malware/adware, if installed on your Mac.

     For instructions:  Install Malwarebytes for Mac          Uninstall Malwarebytes for Mac

     Click the “Scan Now” button. Once done, quit Malwarebytes for Mac.

     Restart the computer and relaunch Safari holding the shift key down.

     Remove unknown profiles (1), unknown login items(@) unknown extensions(3), reset search engine (4)

     and reset Homepage (5 & 6)  listed under Additional steps.

2. Additional steps to take, if necessary.

  1. Remove unknown profiles.

      System Preferences > Profiles

      Open System Preferences, click the “Profiles” icon ( a checkmark on a gear) .

      When Profiles pane opens, select the unknown profile and click the minus button at the bottom.

  2. Remove unknown Login item.

       System Preferences > Users & Groups > Login items

       Authenticate and unlock the lock.

       Highlight the unknown login item and click the “-“ button at the bottom left to remove it.   

  3. Remove unknown extensions:  Safari > Preferences > Extensions

      https://support.apple.com/guide/safari/use-safari-extensions-sfri32508/mac

  4. Reset search engine:    https://support.apple.com/guide/safari/customize-your-search-ibrwe75c2a3c/mac

      Change Home Page

  5. Reset  Homepage.   https://support.apple.com/guide/safari/set-your-homepage-ibrw1020/mac  

      Section: Check other browser settings.

   6. Ref: https://forums.malwarebytes.com/topic/236261-how-to-remove-weknow-malware-and-others/

   7. Shutdown the computer from  menu. Start your Mac using the Power button.

 If necessary, follow the manual instructions.  Do not download any other programs that are listed in the articles.   

See if the below helps. I would scroll down to the below or you might fall asleep.

Step 1. Eliminate Yahoo Redirect from Windows

Step 2. Delete Yahoo Redirect from Mac OS X

Step 3. Uninstall Yahoo Redirect from Internet Explorer

Step 4. Remove Yahoo Redirect from Microsoft Edge

Step 5. Erase Yahoo Redirect from Mozilla Firefox

Step 6. Get rid of Yahoo Redirect from Google Chrome

Step 7. Eliminate Yahoo Redirect from Safari

https://www.2-spyware.com/remove-yahoo-redirect-virus.html