How muscular should a guy be to be attractive?

I have a body that looks kind of like this:

How muscular should a guy be to be attractive?

And I would like to get more defintion in my upper body. Especially my shoulders. But otherwise I don't see myself getting muscular. I don't have the level of commitment. Can having less muscles like this still be attractive?

How muscular should a guy be to be attractive?
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