Proven solution for Bing search hijacking?

You could try the Malwarebytes forum or try contacting Support.

https://support.malwarebytes.com/community/mac

Try running this program in your normal user account, then copy and paste the output in a reply. The program was created by etresoft, a frequent contributor.  Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy Report” and then paste into a reply. This will show what is running on your computer. No personal information is shown. If the log won’t post, try posting it in Pastebin and provide a link in a reply        Pastebin

Etrecheck – System Information    10.10 and later

Yes, the Bing redirect has reared its ugly head again and in a slightly different form. It seems the affected files can be renamed randomly making detection more difficult. I'm going to ask some of our more experienced malware experts to jump in here if they have any advice.

Have you tried the May updated instructions?

Not promoting any of the Downloads available on these sites...

https://macsecurity.net/view/226-bing-redirect-virus-mac

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