I’ve been using Macs since 2009 for programming and have always used _by default_ Option+arrows in all apps for jumping between words and Cmd+arrow for beginning and end of line/file. I have never experienced “fn” to be used for moving the cursor around. It’s interesting that you had a different experience since these have been OS defaults and you can change them of course. I wonder if these was another software which messed with your shortcuts?
The things I remember using for work back then was eclipse, Textedit(not sure about the name, but at least the simple text editor that came with Mac), Safari, Firefox and Chrome.
Eclipse, Firefox, and Chrome use non-native text controls to varying degrees. That may have been your issue. Apple can’t do anything about bad third-party software.
