It depends entirely on the industry and job of course. Managers (and owners) prosper or not based on a number of factors, one being their ability to hire and retain employees that bring value to the company in excess of their costs.

A manager considering it for something like a software dev position would just be hurting themselves, though likely only a little as I doubt ‘candidate wears plaid’ comes up often.

If it was someone hiring for a fashion designer position, or a public facing spokesperson position, plaid could be a huge plus or a huge minus (I’m guessing huge minus as of right now for most), and what the candidate wears and how the they present themselves relative to current fashions and norms is a huge and important element that the hiring manager would be incompetent to not consider.

That said, there are plenty of managers who are pretty incompetent.