This is a very unusual plate. The decorations and colors look like nothing I have seen. It does not show a lot of wear. Does it look right to you for a mid 19th century plate?
Despite the Xianfeng mark and the Chinese motif there is nothing traditional. Late 20th to 21st century made, in my view. You have to look for age signs and should accumulate some basic knowledge of how antiques look, otherwise you will keep obtaining items with no collecting value. This item can impossibly be antique, if judged by shape, colors and new look.
The Chinese usually say you have to spend 10% of what you buy on literature, for study. Today the Internet can replace part of the books, but looking at Ebay and other commercial items will get you nowhere, I'm afraid.