There was a time when my cat owned three cardboard boxes, and whenever I wanted to take the old cardboard boxes that he had bitten through, he would chase me and meow in opposition.
Masking tape. It's paper and glue, eco and cat friendly and will provide him the structural support today's modern feline requires in loungewear accessories.
Based on the fuzz on the torn corner, he likes rubbing on the broken box. I’d leave that one for him for a while as-is, replace it when he doesn’t use it anymore.