You no longer have to hold Shift to maintain proportions when transforming most kinds of layers. Prior to CC 2019 you had to hold Shift when transforming to maintain the original proportions. Check on Use Legacy Undo Shortcuts and click OK.If you don’t like the new keystrokes, you can revert back to the prior behavior as follows:

Miss the old toggle-style undo? Use Cmd–Opt–Z (Mac) or Ctrl–Alt–Z (Windows).

To redo, you now hit Cmd–Shift–Z (Mac) or Ctrl–Shift–Z (Windows).

In CC 2019 each time you hit Cmd–Z (Mac) or Ctrl–Z (Windows), you will go farther back in your file’s history.

CC 2019 changes the keystroke to work like InDesign, Illustrator, etc. Regardless of the reason, it did make Photoshop different than other Creative Cloud apps. It was useful to compare the before and after states to see if the retouching/color correction you just applied looks good.

I always thought this was because of Photoshop’s roots in photography.

It would undo, and then redo the very last thing you did. Prior to Photoshop CC 2019, Cmd–Z (Mac) or Ctrl–Z (Windows) acted as a toggle. Each year Adobe comes out with new features, so what changed in Photoshop CC 2019? We’ll cover the most important changes we think you should know about.

Photoshop cc 2019