1. Use the latest release of MalwareBytes for Mac to remove malware/adware.
Install guide: https://support.malwarebytes.com/docs/DOC-1817
Uninstall Guide: https://support.malwarebytes.com/docs/DOC-1190
The installer may ask you to allow it in Security & Privacy /System Preference. Allow it.
Click the “Scan Now” button. Once done, quit Malwarebytes for Mac.
Restart the computer, relaunch Safari holding the shift key down.
Additional steps, if necessary.
1. Remove unknown Login item.
System Preferences > Users & Groups > Login items
Authenticate and unlock the lock.
Highlight the unknown login item (Mac Mechanic?) and click the “-“ button at the bottom left to remove it.
2. Remove unknown and third party installed extensions.
https://support.apple.com/guide/safari/use-safari-extensions-sfri32508/mac
3. Reset search engine. https://support.apple.com/guide/safari/customize-your-search-ibrwe75c2a3c/mac
4. Reset Homepage. https://support.apple.com/guide/safari/set-your-homepage-ibrw1020/mac
5. Restart the computer, relaunch Safari holding the shift key down.