I'm trying to UV unwrap this door I modeled and really struggling, I don't understand why the UV looks wonky.
Any help would be appreciated.
Sometimes you need to be willing to spend a few minutes editing the UV's after the first unwrap.
Your DoorUVunwrap.blend contains one material called "Steel" suggesting that your door is supposed to be a metal door. The geometry and UV unwrap of a metal door would be a little different than that of a wooden door. The front and side panels of a metal door would probably be pressed from a single sheet of metal where as a wooden door would be made from many different pieces of wood, vertical, horizontal and panels in-between. A single metal pressed sheet is going to require more hand editing of the UV's than a wooden door because the wooden door will have many more UV seams / UV islands and so will unwrap better. The single UV island of the front of the metal door will require some straightening of the UV edges. Knowing this then it is a good idea to keep the geometry as low poly as possible. Less vertices means less UV vertices to straighten out later.
1: Construct the door using as few vertices as possible. In the example below the metal door has half as many vertices compared to your original door.
2: Mark the UV seams in such a way that the back panel will be separated from the front and side panels.(UV seams around the the outer edges of the back panel and along the 4 corner edges. see image below).
3: Select All and UV Unwrap using the Conformal method.
The UV's will need straightening, aligning edges to either the X or Y in the UV space. Sounds a pain but doesn't take long.
4: Start by selecting a line of horizontal edges near the middle and running across the UV island. With the edges selected RMB to open the UV Context Menu and choose the Align Y option. With the edges still selected hit the P key to Pin these vertices. Pinning will stop these vertices moving when we do a second UV unwrap.
Repeat for a second Line of horizontal edges.
With the mouse hovering over this UV island hit the L key to select it all followed by U and choose the Unwrap option.
With all the UV island still selected hit Alt P to Unpin the pinned vertices.
Repeat step 4 for two vertical line of edges. see gif below:
The result should be something like in the image below. If some edges are not quite straight enough you can go in and select lines of vertices and align them as needed.
Below is an example of the same door but "made of wood". Different geometry and many more UV seams. For the wooden door add seams in such a way that each section of wood is isolated from its neighbour. This doors UV's should UV unwrap without later needing to straighten any edges. But the islands may need to be oriented correctly to align with the grain of the wood texture being used.
Modified Blend file: https://blend-exchange.com/b/K1e3Omn8
I may be wrong but it looks like Blender can't unwrap orthogonally (maybe there's an addon for this but UV Squares doesn't seem to do it):
So maybe switch to front view and unwrap with the Project from View option:
The problem is that it will stretch the image texture on the side faces, if it bothers you you can still unwrap these faces apart but it may be tedious to make them match with the front faces.