Monstera Black Spot On Leaves. You asked about washing the leaves. For more info read 4 Signs Your Monstera Is Over-Watered here.
The soil is a bit moist but not too much i think. These discolored areas are a sign of rotting which happens when your plant gets too much water exposure. As a soil-borne fungus its present at all times even deep winter.
The roots need oxygen and if the soil is too wet they can rot.
If the blackening of the leaf plates was not completely then in order not to cut out the entire sheet cut off only the blackened part. Green leaves will not return to black leaves and they should be trimmed. As a soil-borne fungus its present at all times even deep winter. These discolored areas are a sign of rotting which happens when your plant gets too much water exposure.
