IDW has been publishing Dungeons & Dragons comics since 2010 (see "IDW Launching 'D&D' Comics"), and BOOM! Studios acquired the license for Magic: The Gathering comics in 2021 (see "BOOM! Gets 'Magic: The Gathering'"). The Dark Horse announcement likely means that both publishers have lost those licenses.
Dark Horse has collaborated with WotC previously: In 1998, they published a four-issue Magic miniseries that was collected into the graphic novel Magic: The Gathering – Gerrard's Quest, and Dark Horse published a D&D/Stranger Things crossover series in 2020.