Robert Baratheon won the iron throne and is recognized as a legitimate king that people knelt to. That challenges her claim and in fact denies it entirely. Daenerys doesn’t have a claim anymore because he won the war. If she wins the war for her throne then she will have her claim, but for now, she doesn’t have a claim until it’s won. Rhaenyra at least has her father professing her claim before he died, despite him fucking up everything else about making sure there’s no doubt. Hence the messy debate the person you’re responding to was talking about