If f(n) = Ω(n) and g(n) = O(f(n)), what do we know about g?
Knowing that $f(n)=\Omega(n)$ and $g(n)=O(f(n))$ doesn't tell you anything about $g(n)$. For all we know, $f(n)$ could be $2^{(2^{(2^n)})}$ and then $g(n)$ could be almost any function. All we know is it is upper bounded by some function, which might grow arbitrarily fast. It's akin to saying "up to 50% off or more".