Obviously Duncan will be a huge flop, but if he can pull 1-2% in Georgia that could swing a state.
The question is whether the Trump-skeptical Republicans who vote for him are people who otherwise would have cast reluctant votes for Trump, or reluctant votes for Biden. I would lean toward No Labels hurting Biden more generally, but it's possible just in Georgia with a guy that Republicans have previously backed, he might hurt Trump more.
I could see Duncan taking more from Trump than Biden here. There's a large "normal" subset of the state GOP (the type of voters who supported Brad Raffensperger, for example) and he's well respected by them. I'm sure he'd be a non-factor in every other state.