In my case, I had installed a new installation of MYSQL(8) and WORKBENCH etc. so that I could then work on an old WordPress website. No matter what I did, it wouldn't work. Kept getting "ERROR ESTABLISHING CONNECTION" etc. Thinking that it was maybe something to do with WordPress(since it is old), I tried a basic manual connection with PHP and nothing.
Eventually, I figured out that I had to downgrade MySQL. So I went back to MYSQL installer, found the server, and downgraded MYSQL from 8.0 back to 5.5
As soon as I did that, everything worked.