Is carbon dioxide formed during incomplete combustion of methane? ... ?

Incomplete combustion occurs when the supply of air or oxygen is poor. Water is still produced, but carbon monoxide and carbon are produced instead of carbon dioxide. The carbon is released as soot. Carbon monoxide is a poisonous gas, which is one reason why complete combustion is preferred to incomplete combustion.

Yes ... of course but comes along with CO ... that is carbon monoxide.

carbon di oxide is formed by complete combustion of methane. carbon monoxide is formed by incomplete combustion.