From a person with a lot of years of experience fighting mold on wood in a humid climate, what you want is borax:
https://www.thisoldhouse.com/green-home/21331232/killing-mold-on-wood
Borax kills mold and also soaks into wood and stays there to prevent future growth. Bleach does not help on porous surfaces like wood:
"Note that bleach should not be used to kill mold found on wood. While bleach is very effective for killing mold on non-porous surfaces, it doesn’t work well when it comes to wood. This is because the chlorine in bleach can’t penetrate wood, so only the water portion of the bleach gets absorbed.
The mold may appear to be removed from the surface, but it’ll likely continue to grow underneath and return within a few months."
Deep cut Expanse reference. Specifically to an episode that had a lot of personal meaning for me.