It's true that thanos, afaik, has never been shown destroying a star. It is false to say that this is not possible for him, just as it would be false to say that he cannot pour himself a cup of tea (though this also has never been shown). Heralds can destroy stars -- this is essentially the type of work they are designed for -- and thanos' cosmic energy blasts have been shown to be more powerful than theirs.
Any being who can hurt a normal-powered galactus and tyrant with cosmic blasts, who can ko herald-levels with ease, can destroy a star.
Superman and thanos fight in different leagues. Sun-dipping superman does not turn him into a skyfather. He lost to a probably sub-herald enemy while sun-dipped, an enemy who was unable to escape the gravitational pull of the sun (much less destroy it). That does not bode well for him in a fight with someone in thanos' power class.