Magic Trackpad drag lag on external displays after macOS 26.5 update

HNEDGW wrote:

After updating to macOS 26.5 (25F71), dragging operations (text selection, window moving, rectangle selection in Finder) with an external Magic Trackpad are noticeably laggy ONLY on external displays.

Environment:

- MacBook Pro (Apple Silicon)

- macOS 26.5 (25F71), updated on May 18, 2026

- Magic Trackpad (tested both Bluetooth and wired USB)

- Two 27-inch external monitors (DELL P2725DE)

What works fine:

- Cursor movement (1 finger) → smooth

- Scrolling (2 fingers) → smooth

- All operations on built-in display → no lag

- All operations with built-in trackpad on external display → no lag

What is laggy:

- Any drag operation (3-finger drag, physical click+drag) on external displays when using the external Magic Trackpad

- Affects ALL apps including Finder

- Selection highlight lags behind cursor movement

- This ONLY happens with the external Magic Trackpad — the built-in trackpad works perfectly on the same external displays with the same apps

Troubleshooting already tried (none helped):

- USB wired connection (not a Bluetooth issue)

- defaults write NSWindowHasShadow -bool false

- defaults write -g NSAutoFillHeuristicControllerEnabled -bool false

- Deleted windowserver plist files

- Disabled "Displays have separate Spaces"

- Quit Karabiner-Elements

I believe this issue did not exist on macOS 26.4. It started after the 26.5 update.

Any workaround or fix would be greatly appreciated!

Clearly stated.

< Karabiner-Elements > this caught my eye;

Did you try the basic trouble shooting for narrowing down an issue:

—A SafeBoot Start up your Mac in safe mode - Apple Support will sort many anomalies

This test will tell you if third party interference; most extensions etc are not loaded in safe boot mode.

—Test issue in another user (or guest user) account Change Users & Groups settings on Mac - Apple Support

This will tell you if it a universal issue or isolated to your user/admin account. 

This seems a long shot —

there have been some known oddities with "cursor set to a larger-than-normal size as well as custom color" as odd as it seems.

>System Settings>Accessibility>Pointer recommend reset defaults and compare your results.