I've been using an iron fishing rod with a golden lure and luck of the sea III, but all i catch is fish, and very very rarely a few trash items like bowls and the wooden chest, why can't i catch anything better like enchantment books, and the better chests

You can, you´re just unlucky :)
Make sure you´re fishing in open water, as that´s the only place you can get treasure (Change in vanilla in 1.16 I believe)

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That was my issue, i was unaware of that change in 1.16 and now my loot is much better with open water