After updating to macOS Tahoe(version 26), many users have reported their Macs becoming extremely slow and sluggish. Window animations stutter, the cursor lags behind, and apps like VSCode, Slack, Cursor, Chrome, and even Adobe apps can cause the fans to ramp up or the system to freeze temporarily.
After updating my Mac to macOS Tahoe 26, I noticed that after a few hours of use, the system would feel slow, heavy — opening or dragging windows wasn’t as smooth as before. I often see the spinning globe/wheel icon and my Mac freezes. I press the ⌘ Command ⌥ Option Esc keys to unfreeze and quit the problem app. Restarting also helped temporarily, but the sluggishness returned after a while.
Generally, the experience has been terrible after macOS 26 update. After a few hours of use, restarting becomes imperative. The mouse pointer and windows lagging behind every click and drag, sometimes appearing and disappearing randomly all over the desktop.
Why macOS Tahoe Feels Sluggish
According to multiple developer reports and GitHub discussions, macOS Tahoe has a bug related to window rendering and GPU performance, especially affecting Electron-based apps such as VSCode, Slack, Discord, and others. Here’s what happens:
- macOS 26 introduced a new rendering behavior that causes the WindowServer process to consume a lot of GPU power when certain apps are open (even if they’re in the background).
- As a result, macOS may become slow to respond, with delayed clicks, laggy scrolling, and higher fan activity.
- The issue affects both Apple Silicon and Intel Macs, though it appears to be worse on Intelmodels.
Developers traced part of the problem to a feature called AutoFillHeuristicController, and another to window shadows used by Electron apps.
Fix 1: Disable AutoFill Heuristics
The first solution you should try if you are Mac is slow after macOS Tahoe update is to disable autoFill heuristics. This fix targets the input lag problem that builds up over time in many apps. Open Terminal and run this command:
defaults write -g NSAutoFillHeuristicControllerEnabled -bool false
Then restart your Mac (or log out and back in). Note: This disables macOS’s built-in autofill feature system-wide, which may affect form or text autofill in some apps.
If you ever want to undo this change, run:
defaults delete -g NSAutoFillHeuristicControllerEnabled
and restart again.
Fix 2: Disable Window Shadows for Electron Apps
The second bug causes heavy GPU usage when apps like VSCode, Cursor, Slack, or Discord are open. You can disable the shadow rendering feature temporarily with this command:
launchctl setenv CHROME_HEADLESS 1
This helps reduce GPU spikes and improves responsiveness. However, you’ll need to run this command again after each reboot, as it doesn’t persist automatically.
If you prefer it to apply at login, you can create a simple Launch Agent or use tools like EnvPane to set environment variables on startup.
To revert the change, restart your Mac — the setting automatically resets after reboot.
Fix 3: Restart WindowServer manually (temporary relief)
If you don’t want to use Terminal commands above, you can restart the WindowServer process to temporarily refresh performance:
sudo killall -HUP WindowServer
This logs you out, so ensure to save your work first.
It clears GPU and input lag for a short while but doesn’t fix the root cause.
And lastly, I recommend resetting NVRAM after updating to Tahoe reduced thermal and fan issues slightly
