What people think of as “mold” is often endophytic or mycorrhizal fungi that quickly consume dead parts of cuttings when put in high humidity conditions. It is white and fuzzy (molds change color when they begin producing spores), and may sometimes “burst” through the lenticels when the cutting is too wet/not getting enough air. When I tried tissue culture with dormant fig buds they all had this beneficial/benign fungi pre sent, even after sanitation with bleach.
While there are some pathogenic molds, most I’ve seen on cuttings are harmless and growing on the surface only, feeding off of sap residue, they can simply be wiped off if they worry you.
Pathogenic microorganisms are easy to detect even though they are often invisible to the naked eye because they destroy tissue, the bark will discolor, turn slimy and slip off with hardly any pressure. Aside from systemic fungicides there is nothing to do but remove the affected part back to healthy wood because the pathogen is inside of the cutting already at that point.
The chemicals given off by fungi and bacteria attracts fungus gnats, which are also blamed for the demise of cuttings when the real issue is ignored. The larvae can damage young roots and spread pathogens, however, they are not physically equipped to feed on woody tissues until after bacteria and fungi have begun decomposing them, the larvae are feeding on the fungus, not the wood.
It is not possible to sterilize either the cuttings or the rooting media (and keep it sterile anyway) fungi and bacteria spores are literally everywhere. It is not recommended to sterilize organic mixes because that creates a “biological vacuum” which can be quickly populated by pathogens because they face no competition from beneficial or benign microorganisms.
Most often the problem is defective cuttings (freeze damage, improper storage), these may appear OK at first but deteriorate rapidly. Next most likely is too much water and not enough fresh air, a small fan for air circulation or waiting until outdoor conditions are right will solve that problem.