Home HVAC Question, Is this normal?

We are going to need closeups. Is that a register opening in the ceiling?

Black mold in a return vent?

You can have all that cleaned.

If it is fungal growth, it is coming from condensation, you have gaps in the ducts allowing hot air and cold air to mix...

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Like others have said, flex duct and those spots you are seeing are likely just dust/dirt that made it past the filter on the return air, especially if the ductwork is a few years old

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Looked like mold at first glance and it may be more or less but also seems kinda dry and stiff to the touch. I checked upstairs around the things and stuff and don’t see any signs of moisture, clogs or anything.

Welcome to LA. People get all bent out of shape and scream about "MOLD!!!" in a house here. As I heard a PhD LSU Professor say one time, "show me a place in LA outside of a lab that doesn't have mold."

Not a return vent. Supply drop this isn’t a big deal

YOU have as all AC systems do an evap coil on your system. When the humidity is removed in the coil condensation builds and that's where the water draining outside the home comes from. Moisture with darkness plus flow of air equals fungi growth. It originates in the coil box air flow carries it through your system. It can be cleaned however be cautious as to who you hire. This service has been the focus of many allegations of poor business ethics.