Let's first describe how it is on PC where I play the game: If I hover over an object, the mouse curser changes it's shape into the symbol of the action I will do. On ordinary barrels it is an open chest for looking inside. On barrels with oil, water or explosives it's the sword which is the gaming world- wide understood symbol for attack. I know it from several RTS games too. And if the symbol is highlighted in red it indicates that bystanding NPCs will disapprove your actions.
So the UI does express what you will do. If you watch carefull enough. If the curser is too small for you to see it, there is for sure a setting somewhere to enlarge the cursor. Or maybe a mod.
My impression is that you biggest problem here is to understand that those objects are no containers. So there is no option to look inside.
It's not an UI issue but a handling issue.
since dragging into inventory may fail due to overload issues this can't be default action neither.
And under certain circumstances you may want to destroy a barrel. To spread oil or water in preparation for a battle.