Is this fix confirmed for macOS Sequoia 15.x?

Yes — verified on macOS Sequoia 15.x. Article is updated when Apple ships a point release that changes the symptom or fix.

How to Fix Missing Window Tiling Previews in macOS Sequoia 15.x

Q: How do I fix Missing Window Tiling Previews in macOS Sequoia 15.x?

Three approaches in order of safety: (1) Reset WindowServer; (2) Re-enable via Defaults. Full Terminal commands and System Settings paths are inside each section.

Symptom: You drag a window to the edge of the screen in macOS Sequoia (15.x), but the ghost-like "preview" rectangle never appears and the window won't snap into place.

TL;DR fix

Save your work, then in Terminal run sudo killall WindowServer — this logs you out immediately and restarts the tiling engine. After logging back in, snap previews should reappear. If they don't, run defaults write com.apple.WindowManager EnableStandardClickToShowDesktop -bool true && killall WindowManager.

Why this happens

The "WindowServer" process responsible for Sequoia's new tiling engine can crash or become disabled by a corrupted configuration file.

Fix 1: Reset WindowServer

Warning: This will log you out immediately. Save your work.
Open Terminal.
Run:

sudo killall WindowServer

Fix 2: Re-enable via Defaults

In Terminal:

defaults write com.apple.WindowManager EnableStandardClickToShowDesktop -bool true

killall WindowManager

Tested and documented by the MacDebug team — about MacDebug. See also Widgets Not Loading on Sequoia, Private Wi-Fi Address Issues on Sequoia, or browse all guides on macdebug.