How do I stop unwanted ads on Safari?

 1. Remove 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.

     Repeat the scan couple of times.

 2. Additional steps to take if necessary (1) 

  1. Remove unknown extensions:  Safari > Preferences > Extensions

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

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

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

  4. Restart your Mac. Relaunch Safari holding the Shift key down.      

3. Additional steps to take if necessary (2)

   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. Try an Ad blocking extension.

Click Safari in the menu bar and then "Safari Extensions".