Bugs after latest update - cannot scroll on my Wix developer to log off, + FB issues

I recently updated (thinking security), but there are increasing problems with functionality on Wix developer page: cannot scroll to log off, even on reload. And on FB, where text editing capacity is erratic.
Overall, the browser is slower to load pages. This may be connected to security, because both Wix and FB are interested in tracking, but I do need to be able to use those sites (I have 4 websites on Wix to manage and edit)
Any fixes out there? I’m on an older Macbook Pro still running High Sierra. OS update is not in the cards - I have specialty software installed that is not supported by later OS.
Thanks!