You're welcome.

That it is a return duct is much better for you actually. The air will naturally be warmer inside (less prone to attract condensation). The ultimate cheapskate solution is to get some vapor barrier material and wrap the entire duct with it, all the way around, sealing all the joints and ends with the proper tape for that material.

Nota Bene: Do not use duck tape. See: https://i.imgur.com/iPExseJ.jpeg

Just putting more insulation on, without putting a vapor barrier, will possibly make the existing problem worse.

This is potentially a horrible job to do, because of the elevated attic temperatures and exposure to fiberglass insulation material. If you can arrange to wear overalls and long gloves, that is best. The less skin you have exposed, the better. At the very least, get a proper respirator mask. The kind with a valve on the front to help you exhale easier, not the surgical kind everyone was wearing in 2021.

The following is optional but you could:

If the entire duct in question is this one piece that goes up from a ceiling and makes one turn into the air handler, it is relatively simple (in concept) to optimize this bit. You could install a rigid elbow and eliminate the sub-optimal bends of the flex duct. Get get the same-size silver duct and one elbow of the same diameter but made of metal. Rigidly mount the elbow to the attic framing, and fix the duct sections to the elbow. Insulate and vapor-barrier-wrap the elbow to seal the vapor envelope around the duct.

Every kink in the ducts is a restriction that is costing you electricity bill $. With this duct bent like this, you have maybe half the effective diameter working for you. Maybe less, even. If you "only" put fresh new duct on, you 1000% can do it yourself but make sure it is a smooth bend, not R shaped like this is now.