
They 41 people, does that mean that they can't see mimi? Is his soul still trapped in the mask?

No, they can see him.
Li came in a bag together with Mimi. So 2 people on a bag. People can see Mimi. But since 41 are there, they were wondering who was the extra cause that meant that there was an imposter/Extra (Mimi) of which they weren't sure.
The mask seems more a promp to hide his face. it also contains Mimi soul. It's like a body. The reason why Mimi soul fan materialize and fight snakes(begginer of the chapter) is because of that mask.
Hope this helps.
Hope this becomes a good wake up call for him, dude puts himself in danger recklessly, tbh I feel bad for aresh, having to worry over his workaholic ass every time must be tough