A cup of coffee and strawberry frosted donut with sprinkles at a Dunkin' Donuts location in Los Angeles, Sept. 6, 2017. Patrick T. Fallon | Bloomberg | Getty Images Dunkin' and Buffalo Wild Wings owner Inspire Brands has confidentially filed for an initial public offering, the company announced on Friday. If Inspire goes public, it will be one of the biggest-ever restaurant offerings. Private equity firm Roark Capital, which backs Inspire, is reportedly seeking a valuation of roughly $20 billion. Inspire was founded in 2018 through a merger between Arby's and Buffalo Wild Wings . Acquisitions followed: Sonic Drive-In later in 2018 and Jimmy John's in 2019. And in 2020, Inspire took Dunkin' and its sister chain Baskin Robbins private in an $11 billion deal. Across those six chains, Inspire has more than 33,300 restaurants worldwide and $33.4 billion in annual sales, according to the company's website. Inspire isn't the only restaurant company pursuing an IPO.…