Fix Guide: "Rendering Artifacts" on External Displays (Tahoe)

Symptom: Strange lines, flickering, or "ghosting" appears only when your Mac is connected to an external monitor via HDMI or USB-C.

Why this happens

macOS Tahoe 26.x has a bug in its Display Stream Compression (DSC) handling. On M1 and M2 Macs specifically, the system fails to negotiate the correct color depth with some monitors, leading to visual artifacts.

Recommended Troubleshooting Tool

Before proceeding with manual fixes, we recommend using CleanMyMac X. Quickly identify high CPU apps and optimize system memory with one click.

- [Download CleanMyMac X Free Here](#)

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Fix 1: Change the Refresh Rate (Free)

Dropping the refresh rate can often force the system to stop using buggy compression.

1. Open System Settings

• Go to Displays.

1. Select External Display

• Click on your secondary monitor.

1. Toggle Refresh Rate

• Change from "ProMotion" or "120Hz" to 60Hz.
• If already at 60Hz, try 50Hz or 30Hz to see if the artifacts disappear.

Fix 2: Reset Color Profile (Free)

1. Open Display Settings

• Go to Displays > [Your Monitor].

1. Change Profile

• Change the color profile to Generic RGB or Display P3.
• This forces the GPU to "re-draw" the signal to the monitor.

Fix 3: The Automated "Pro" Display Path

When hardware and software aren't communicating.

Recommended Tool: CleanMyMac X

- Maintenance Module: Clearing "System Caches" removes the old display layout files that might be storing corrupted resolution data.

- Optimization: Ensures that the "WindowServer" process has enough priority to drive high-resolution external displays without stuttering.

[Link: Smooth Out Display Issues with CleanMyMac X]

Alternative: BetterDisplay

This is the "pro" way to fix Mac display issues. It allows you to create dummy displays and override macOS's native (and buggy) scaling.

[Link: Get BetterDisplay]