mcafee web advisor addin blocks Duo 2nd factor auth, even when added to trusted sites. Can this be fixed?
it keeps re-enabling
I would strongly suggest disabling anything related to McAfee, and in fact, uninstall it entirely from your computer. Use the built in Windows Defender anti-virus, with monthly scans using malwarebytes (www.malwarebytes.com). McAfee is a generally poor product and can leave you more at more risk.
My broadband supplier is Sky and I get McAfee thro' them
That's fine, you don't need to use it still. All that means is that McAfee paid Sky to tell you to install it.