This is not parallax. It is keystoning. Parallax where it applies to cameras comes in several flavors - in the old days, when the lens taking the actual picture was not the same as the lens (viewfinder) used to compose the image, there is a shift in composition. This was typical of rangefinder cameras and twin lens reflex cameras.

Today, parallax error is used to describe what happens when you take a panorama image, and you do not rotate the camera around the "no parallax point" - and when stitching the image the program has difficulty resolving foreground objects that obscure background objects in the overlapping sections of the pano stitch.

http://fmphotocourses.blogspot.com/2006/12/camera-types-and-parallax-error.html

https://www.outdoorphoto.co.za/blog/understanding-panorama-photography/

The best way to address KEYSTONE distortion is while shooting. This is a common problem in photographing tall architectural structures from the ground. It is especially notable when buildings seem misshapen, look that they are lean over, crooked or falling over or when parallel vertical or horizontal lines seem to converge at an unnatural perspective. Basically, a rectangular shaped structure takes on a trapezoidal appearance in the photograph. This effect is especially present when photographing structures at fairly close distances with a wide angle lens or short focal length setting on a zoom lens.

In commercial/architectural photography the traditional way of correcting this in the camera was the use of a view camera with an adjustable front standard or a medium format or digital camera with a tilt/shift perspective control lens. This enables to keeping the film or sensor plane parallel to the subject and moving the lens, usually upward or downward to accommodate the height of the structure. If you do quite a bit of this kind of work, it pays to invest in this kind of equipment. This would require the use of a tripod and of course, it somewhat time-consuming in setting up each shot.

For more casual shooting as a hobbyist, enthusiast or tourist when shooting quickly and handheld, the best approach is to use one of a few different strategies- all having to do with camera position, placement in relation to the subject.

You can simply keep the camera (sensor) parallel to the subject structure (no tilting of the camer upward or downward) which may result in too much ground or sky in your composition- this unneeded space can be cropped out in post-processing. Of course, you are gonna need the distance. If possible, you can try to use a normal or moderately wide focal length. Attached, is a page out of an old Kodak Professional Photoguide that explains some f this theory in detail along with diagrams. This applied to 35mm cameras when view cameras or P/C lenses are not used- it applies to current digital equipment.

Another method that I use is to find higher ground or access that will enable me to shoot from about halfway up the subject structure. Sometimes a hill or natural elevation will do the job. I have shot from rooftops or windows of nearby buildings. On commercial jobs, I have used a cherry picker, other elevation device or a simple stepladder. This method makes for fast easy handheld shooting, exact composition without fussing with view camera or P/C adjustments.

Sometimes, no matter what you do or where condition are especially difficult, some post-processing correction will be required. Most of the popular software such as Lightroom and PhotoShop have some perspective control adjustments. Since I address most of my perspective control in shooting, I use a simple app that I can access on my tablet and make the adjust right on site so I know I have everything under control before I leave the location. See a screenshot of the app- there are two simple arrows to indicate the direction of correction and the rest is totally visual- line up the vertical lines with the grid lines on the screen. As with any perspective control or image rotation in post-processing, you will lose a few pixels. You will also lose a few in cropping out excessive ground and sky but nothing too seriously impair the image quality if out have a good composition where the main subject is dominant in the image space.

I do quite a volume of exterior and interior work for advertising clients. The same principles apply to interior work. Sometimes I have to work quickly in homes or hotel rooms that are still occupied by the residents so I can't get into complex setups. In an average room with an 8-foot ceiling, I place cameras at 4 feet and crop afterward. In one of the shots posted here, I had to use a view camera because the shot was made for the flooring company and a low angle was needed to emphasize the floor and force more depth of field.

Sometimes when shooting from high places aircraft, you can get a different kinda keystoning. When you shoot downwards, especially with a wide angle focal lengths, you get foreshortening. This makes structures seem large at the top and tapered toward the bottom- so you apply some of the aforementioned methods in reverse. Wh shoot full-length portraits, make sure the camera is at the subject's waste level otherwise they will appear shorter than they are.

Oh- Sometimes Keystone is a good thing. It gives dynamic lines to tall modern structures. Theses are not architecturally correct but they make for nice advertising shots and annual report covers. I hope this helps!

I reiterate-

Defs:
1. the apparent displacement of an observed object due to a change in the position of the observer.

3. the difference between the view of an object as seen through the picture-taking lens of a camera and the view as seen through a separate viewfinder.

Obviously you are referring to #3.

I used #1. the building is displaced, or angled back.

And I found this:
The keystone effect is the apparent distortion of an image caused by projecting it onto an angled surface. It is the distortion of the image dimensions, such as making a square look like a trapezoid, the shape of an architectural keystone, hence the name of the feature.
In photography, the term is used to describe the apparent leaning of buildings towards the vertical centerline of the photo when shooting upwards,...

Parallax≈Keystone Effect.
But, lets not quibble over semantics, eh?.

In 45 years, no one I know ever called it the keystone effect, always parallax.

Insisting on your interpretation of parallax as being equivalent to keystone effect, doesn't make you right - a building depicted in an image as having a third point of perspective - the vertical one - when you take a picture with a camera with a wide angle lens pointed up towards the building is not a "displacement" - the building has not moved, either in reality or perceptually. In parallax, using your own definitions, there is no displacement and there is no parallax due to using two viewing devices.

If you want a real example of parallax, close both of your eyes. Open one, note where everything is. Close it and open the other. Is EVERYTHING is the same relative position as when you were looking at the scene with the other eye? No, it is not. especially if you have near and far field objects in view. This is one way to demonstrate parallax. Your interpretation is unique, and it falls under the category of opinion, which everyone is entitled to, but not fact, which simply cannot be argued with. This is not semantics - you are misusing commonly used terms to make your point. Bottom line. you are being quite silly.