Search Marquis

Go step by step and test.

   1. Remove unknown profiles if present.

      System Preferences > Profiles

      Open System Preferences,  select “General and 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.

      Section: Remove a configuration profile from your Mac

      Profiles: https://support.apple.com/guide/mac-help/configuration-profiles-standardize-settings-mh35561/mac

  2. Remove unknown extensions:  Safari > Preferences > Extensions

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

   3. 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 v4      Uninstall Malwarebytes for Mac

       Click the “FREE DOWNLOAD” button.

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

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

       Scan for Malware again.

       Additional steps  if necessary.

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

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

  6. Check proxies. SOCKS?

      System Preferences > Network > Advanced > Proxies

      Deselect   any  proxies if selected.   

   7. Restart the Mac. Relaunch Safari holding the Shift key down.