bing suddenly became my default search engine for safari and I can't get rid of it.

 1. Remove Adware installed on your Mac

     Use  the latest release of Malwarebytes for Mac to remove malware/adware 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.

 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.