Usually mold or wood rot is easily recognizable by the telltale dark soggy patches that form around the door frame.
Garage door frame rotted.
Some garage doors are.
To repair rotted door frame first remove rotted wood with a 5 in 1 or other sharp tool.
Insert the tip of a flat crowbar under the trim.
How to use epoxy on wood for repairs.
These dark spots are caused by the growth of fungi as they feed on moist wood.
Then coat the rotted door frame area with wood hardener as shown.
Mix polyester wood filler or bondo wood filler and press it into the recess with a putty knife.
The main cause of rotted garage doors is water damage.
Wood garage doors tend to absorb all the water and start expanding.
Drafts around the exterior door.
Tap on the back of it with a hammer to drive the tip in as far as you can.
With time the wood frames and bottom starts rotting and breaking down.