Janky as it sounds, the cardboard box idea has merit.
I run two printers in a closet with a door that has gaps at the top, bottom and sides. Not even close to airtight. I installed a HEPA-filter air purifier inside. When I print, I run the purifier on high and use a towel to block off the gap along the floor. It’s not perfect, but it helps substantially. Anecdotally I’d say it reduces what I can smell outside the closet by about 90%.
My partner always used to complain when I was printing, now she finds it quite tolerable. Also helped win her over to the machines once we found items she was interested in printing herself and taught her how to use the equipment.
Here are some more professional-looking examples of what others have done: