Ted Olson, an attorney for Bush in the hanging chad case said Trump doesn’t have a case.

"He said Trumps arguments have to do with unfounded allegations of voter fraud"......this is false

"and not defective ballots,"....this is ambiguous, defective how? there is an ambiguity fallacy

You could say, Person A says "a lawyer said....therefore it's true" It would be an argument from authority fallacy

If person A, "there wasn't ballot fraud....here's one lawyer that agrees"....confirmation bias

As Dr. Bo said, you haven't posted an argument like....

Voter fraud is illegal....Trump says there's voter fraud. Lawyer from "bush chad case" says there's no evidence of fraud...So Trump is wrong...

Then fallacy could be argument from authority, maybe confirmation bias.

There is no argument here; it is just a legal opinion. So no fallacy.

From what you wrote, Olson appears to just be stating a fact - a difference between the two cases. If he said (or implied) that simply because Trump's case does not have to do with defective ballots then it is not "legitimate," he would be wrong legally/factually.