Vinegar will kill mold but it stinks,
hydrogen peroxide will also kill mold and it doesn’t stink.
Is there a concrete wall behind the Sheetrock ?
Concrete walls can be a source of moisture.
Moisture and sheetrock equals mold believe me I live in Oregon we know mold and slugs.
If you are concerned get a dehumidifier in there to help dry things out remove the moisture and the mold will go dormant.
The additional positive about hydrogen peroxide it will bleach the mold especially at higher concentrations +7-12% range will turn blue jeans into painters whites ok I never spilled that much but it will take the color out of fabric.
Once the mold is taken care of and the sheet rock is dried it needs to be painted a good oil based primer is what I use you need to remove the loose paint for best long term results.
If moisture is entering from outside the moisture needs to be stopped or this problem will get worse. In any case the source needs to be stopped.
Just a note, some folks think all molds are bad, there are only a few toxic ones but they do indicate moisture problems.
It appears that the Sheetrock paper has been removed in a small section Use caution there because this paper is part of the strength.
Peal the loose paint, kill the mold , dry the area ( dehumidifier & fan) , I would get some white wall paper and repair the missing paper area , when dry and sanded prime and paint.