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?