Yes Sterno cooking fuel does produce some carbon monoxide when using it.
So you should not use Sterno cooking fuel indoors and should only use Sterno cooking fuel in well ventilated areas to avoid carbon monoxide poisoning.
Any type of fuel used for heating or cooking produces carbon monoxide when burnt and all Sterno is is denatured alcohol that is formed into a jell like state.
That jell like state of the denatured alcohol makes it easy to light and stay lit and helps you easily cook food or heat up things.
I keep Sterno around for both camping and for emergencies if my electric goes out because all I have is an electric stove.
So if the power goes out I can still cook using the Sterno.