Version 20 changed the default behavior so that images scaled proportionally without needing to hold the Shift key. Understanding "Pre-Activated" Software
: Changed the shortcut to Ctrl+Z (Windows) or Cmd+Z (Mac) to match other apps. Adobe Photoshop CC 2019 V20.0.5.27259 Pre-Activated
A high-resolution display (1280x800 minimum at 100% UI scaling). Conclusion Version 20 changed the default behavior so that