How to delete Bing as default search engine from Safari 14.0.3?

If the above doesn't work, you have adware/malware installed. Use  Malwarebytes Anti-Malware for Mac. It may be necessary to run more than one scan. After scanning a couple of times, restart the computer and test. If necessary, follow the manual instructions.  Do not download any other programs that are listed in the articles.  

 https://www.2-spyware.com/remove-bing-redirect-virus.html

 How to get rid of Bing.com Redirect - Virus removal guide

Go to Safari Preferences/Extensions, uninstall any you don't recognize, and then turn all extensions off. Test. If okay, turn the extensions on one by one until you figure out what extension is causing the problem.

Go into Safari, and then click "Safari" at the top left corner of the screen, click "preferences", then select general, and switch the default search engine. You can only switch, not delete.