elementary OS performs the primary action (i.e. open a file) when you click once on an item in Pantheon Files. This single-click behavior can be pretty jarring when many other OS’s rely on the age-old double-click action.
To change the single-click behavior to double-click in Pantheon Files, open dconf Editor (install it from AppCenter if you haven’t already). Then go to
org > pantheon > files > preferences and find
single-click and deselect it.
Now when you want to trigger an action on an item in Files, you have to double-click it.
As a side note, you may be wondering why I offer up tweaks using the dconf Editor instead of GNOME Tweaks or Elementary Tweaks. It’s because I am trying to be a good elementary OS citizen. Daniel Fore has taken a pretty clear stance on such tools: