For the mold on the wall, a solution of white vinegar or a dedicated mold remover can be effective for small, surface-level growth. Wear an N95 mask and gloves. However, since the mold is on porous materials like leather bags and may be inside the wall cavity behind the unit, surface cleaning is often insufficient. Spores become embedded and will return if the moisture issue isn’t fully resolved and the material isn’t properly treated.

Given the spread you describe, a professional inspection is strongly recommended. They can use moisture meters to find hidden dampness inside the wall and assess the full extent. Remediation for a case like this typically involves isolating the area, removing affected porous materials (like damaged drywall), HEPA vacuuming, and antimicrobial treatment to prevent regrowth. For your leather goods, a specialist conservator can advise on salvageability.

To prevent recurrence, ensure the closet door is left ajar for airflow and consider a small dehumidifier or moisture absorber, as enclosed spaces here can trap humid air despite the arid outdoor climate.