Type of board for ceiling in basement staircase?

[raindance]

I have a basement staircase to a basement in a house from 1945. The ceiling in the basement staircase consists of another staircase that is parallel above the basement staircase. On this ceiling in the basement staircase, there is a particle board. The house has been vacant for many years, and mold has developed on the particle board. I plan to replace this moldy particle board. What type of board should I choose? Even though it won't be as humid again, I would like a board that prevents mold as much as possible. The board is 10-12 mm thick and 114 cm x 190 cm. A thinner board would likely work as well since the studs are close together.

 

[raindance]

Could, for example, this board work even though it is indoors?
https://www.jemfix.se/utvändig-gipsskiva-9-5-mm/4132/9026489/

 

[tergo]

According to Norgips guidelines, the panel should not be surface treated or used indoors

 

[raindance]

Appearance doesn't matter much in the basement. The question is why it couldn't be used indoors? Does it emit toxic substances? If the only issue is that it can't be painted, I can use it unpainted. It's good that it has moisture resistance and is moisture permeable.