Huge lags in "spread to show desktop" on extended display

Followed the steps on my M4 Pro MBP running 15.6.1, I am unable to reproduce the issue you are seeing. The one window on the external/extended display (LG 5K:2K) with the Ventura wallpaper flies to the edge of the screen at normal speed, the same speed as two or more windows (or no windows, when just the shaded border appears anyway). A few minutes later, same result – no issue.

So, it seems to be a problem with your system. See if the problem is present when you boot in safe mode, which disables 3rd party extensions and performs some system cleanup.

Start up your Mac in safe mode - Apple Support

Tom304 wrote:

1. OS version: macOS 15.6.1

Steps to reproduce:

Connect your Mac to an extended display (an iPad with sidecar is also fine)

2. Change your desktop wallpaper to Ventura

3. Leave only one window on desktop

4. Slowly spread your fingers on trackpad to show desktop

5.

Notes:

You can also use sidecar on an iPad if you don't have an extra monitor

6. Wallpaper matters. The one that is easiest to reproduce is the Ventura wallpaper.

7. Make sure to spread your fingers on trackpad to show desktop, do not click desktop.

8. Compare the animations of showing desktop with one and two windows open. Two windows is significantly smoother than one window.

9. If you do not see lags, wait a few minutes after you change the wallpaper to Ventura.

Not sure I understand the post— is there a question or an issue here or just posting your experience?

I have not used "Ventura wallpaper since Ventura in 2022—and I certainly do not have lags in "spread to show desktop"

The current stable release of Sequoia including bug fixes, security updates is macOS 15.6.1

Keep your Mac up to date - Apple Support

Keep your Mac up to date - Apple Support

if there is some issue here you can file a bug report / submit your Apple Feedback here: Product Feedback - Apple