The other sections are different actions that appear in the context menu of the steam desktop icon, so that you can launch steam straight into big picture for example. If you just launch steam, just the [Desktop Entry] section will execute.
While in my experience the answer you replied to works, to get the same behavior as what you got in the terminal, you should edit the exec line to something like steam --forcedesktopscaling=2 %u.
If you use the separate actions, you should edit it there as well, but those won’t have any effect on just launching steam.