The reason they make it look so easy, is that they know how these things are put together in the first place.
You can't be expected to do as they do.
Drilling off screw and nail heads can help, but it usually comes down to a bit of this...............
https://www.screwfix.com/p/magnusson-utility-bar-24/9626v
You don't necessarily need a lot of strength. Just pivot the bar in the right place and heave.
Things tend to come away without too much drama.
Don't make the rookie mistake of whacking with a sledge hammer though. It just makes things worse.