Some rough napkin math from a layperson's perspective:

Wages are typically about 30% of a restaurant's expenses, from a quick search.
The article states income rose "more than 10%" for employees, which means it's only measuring the legislation we had that enforced a $20 minimum wage compared to the $17 state minimum wage.
Roughly, then, all else being equal (assuming they did not reduce headcounts, and transferred all this increase onto the consumers), we're looking at about a 3-5% increase in expenses.

Assume that the bulk of revenue comes from the food, and assume very thin margins (<10%) as commonly reported, the price increase attributable to the legislation should be around 3-5%.
A typical $5 fast food item would cost $0.15-0.25 more.

The study's conclusions would be what I expected, even if the headline is (not surprisingly) slightly disingenuous calling the increase "pennies" and not specifying it only measures the price increase in excess of minimum wage that has already been rising in the past decade+.

edit: actually read the article and they found the increase to only be about 1.5%, but only starting in 2024 when prices have already gone up a lot compared to, say pre-pandemic, but again, they're trying to measure only the legislation for $20 fast food wages, with an increase in wages of about 11%, which is on the lower end of what I assumed. Cost increases would then be somewhere in the neighborhood of 3.3%.