Safari hijacked by yahoo search
On my iMac Safari was returning search results from yahoo.com when I did a search on the google.com page.
The problem turned out to be a web proxy. Go into your advanced network settings on the Proxys tab and make sure the Web Proxy and Secure Web Proxy boxes are not checked (unless you know they should be, but for me those had never been used and should not have been checked).
iMac 27″ 5K, macOS 11.2