When we covered the update to macOS 13.3 Ventura in “Apple Releases iOS 16.4, iPadOS 16.4, macOS 13.3 Ventura, watchOS 9.4, tvOS 16.4, and HomePod Software 16.4” (27 March 2023), Howard Rosenman commented that the Aerial screen saver would no longer show on both of the displays attached to his M2 Mac mini. He was right, and others confirmed that the problem afflicted both Apple and third-party screen savers, such as Aerial and Electric Sheep.
I don’t know when Apple fixed the bug because the company didn’t see fit to mention it in any release notes. Regardless, in macOS 13.4.1, the screen saver again works properly with multiple displays. If, like me, you switched your screen saver module because it wouldn’t show on all your displays, you can now return to your preferred approach in System Settings > Screen Saver.
Alas, Apple didn’t tackle the more complex problem of getting the screen saver to display edited or rotated photos rather than the original image (see “macOS Photo Screen Savers Still Don’t Properly Display Rotated or Edited Images,” 5 March 2023).