Should cold air return ducts be sealed?

In terms of sealing a return vent hole, it is enough that the drywall and the uprights are compressed to create a channel in the wall. There is no need to seal the corners, unless there are gaps left. In addition to the supply ducts that provide the air conditioning, there is also a system of return air ducts that return the consumed air to the air conditioning system. To make wall-to-floor transitions, you can cut metal sheets to create a custom accessory (box) and seal the metal joints with adhesive tape or duct sealing putty.