The answer is the first one.
Ironically, it is not an Odd One Out because it is not!
The second is the only shape that is a circle.
The third is the only shape that is green.
The fourth (second row) is the only shape without a border.
The fifth (second row) is the only shape that is small.
Since each one of these is unique in some way, then the answer is the first shape because it is not unique in any way.
It shares a boarder, its color and its shape with other shapes.
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