Dr of BBQ
Tile backer board, is called cement board by professionals in the industry. Brands like Armoroc, and Durloc are common. And it’s mostly fireproof.
But Edwnmax a report of a fire in 1906 come on?
It’s (cement board) approved for kitchens in most any state fire code and often covered with SS or other non porous metal. But I would insulate behind it if I were using it. If you read the other threads (3 or 4 multi post threads) here on this topic the temps at your filters and at your fan, are much lower than anyone would think.
But why do you keep double posting?