My recollection may be incorrect, but it seems like versions of Lightroom prior to 10 did perspective/parallax correction differently.
Moving the Vertical or horizontal sliders would correct vertical or horizontal perspective/parallax issues. It was quite pronounced and appeared to work reasonably well.
In version 10.2 when I move the Vertical slider in either direction it simply makes the vertical taller with ALMOST no effect on the parallax.
Same thing when moving the Horizontal slider. The image gets very wide, but the horizontal perspective correction is almost non-existent.
Did Adobe change something? Is there a preference I need to change? Or is my recollection incorrect?
Nothing has changed and it still works the way it did work for me (I lowered the scale so you can see it well).
Mine seems to be drastically different now. But I don't know why it changed. It USED to look like yours. Now it looks like this:
Here's the original image - ordinary D850 image (I'm testing a lens)
-100 vertical - HUGELY tall, very little parallax correction.
-100 horizontal - HUGELY wide, very little parallax correction.
Same -100 horizontal with the scale to -100 and x position so the whole image fits. I don't recall this happening in previous version of LR, though I haven't had to do much so it may have been like this for the last year. Is there some preference I need to change?
Lightroom gives you a warning in the Transformation panel. What does it say?
What would the warning look like? I haven't seen anything.
All your screenshots show a warning at the bottom of the panel, but it was too small for me to read what it said. That is why I asked. I downloaded a screenshot and now I can just see that this is a warning about resetting the crop, so that is irrelevant.
You won't get a warning if you try to use Transform on images taken with a telephoto lens. You can do that just fine, but the result will be unexpected (as you noticed).
Hmm, my transform doesn't behave that way and behaves like it always has. Does it still do this if you turn off GPU acceleration?
You will see very different whole-picture results from manual controls depending on the focal length ratio / included angle of view. Scene perspective is a matter of angles, and photos are not necessarily interchangeable for perspective unless you've considered and compared the same angles of view within those two. IMO a Guided or Upright method will be found more controllable and usable with a telephoto shot (or a wideangle, differently so).
In my screenshot below, the top photo was with 10mm lens and the lower photo with 135mm lens, both from the same APS-C camera, both given -100 correction of Vertical in the manual transform panel for the right side version. I reduced these using Scale to show what is happening at their edges. The wideangle shot has clear geometric "warping" from the lens profile in addition to the perspective transform.
In fact, while effective results seem different I think the same actual transform is being applied per degree of angle of view. Within just the central part of a wideangle capture, the identical geometry and perspective are found, of what would have been seen with a longer lens. There is no such thing as wideangle or telephoto distortion, aside from this matter of included viewing angle and its consequences. Hence eyeballing the shape result of -100 Vertical for the telephoto shot and overlaying that onto the wideangle shot which also has received -100 Vertical, the two seem to compatibly sit within the same perspective change as below. 100 is an extreme transform, btw.
If you look at what has happened to just the central part of my wideangle shot (inside the green lines) as compared with the uncorrected shot, that has undergone the same extreme vertical stretching seen in the telephoto shots, both the OP's example and my own.
Yes, this could very well explain it. What was the focal length of the lens? Your image looks like it was indeed shot with a long focal length.
I believe that image was about 150mm... I tried it this morning with one from a 24mm and it was better. I don't remember this focal-length-aware behavior in the past, but as long as that's what's going on I won't be concerned that the transform doesn't act as I expect....