Intermittent magenta/black window artifacts on external monitor when “Disconnect built-in display” is enabled

[heungson]

MicrosoftTeams-video.mp4

When using mirroring virtual screen with HiDPI, screen on the external monitor occasionally shows severe graphical artifacts—magenta blocks across windows—whenever the cursor brushes the hidden macOS menu bar.

Steps to Reproduce:

1. Enable automatically hide menu bar option in mac os setting
2. Enable mirror virtual screen and HiDPI on better display
3. Connect an external monitor (USB-C or HDMI).
4. Move the pointer to the top edge so the macOS menu bar slides down.Expected Result:
   The menu bar appears and all windows redraw normally.

Actual Result:
Large magenta/black rectangles smear across window title bars, toolbars, and borders (see attached screenshot or video).
Toggle the built-in display on, then off sometimes clears the artifacts and do not reappear.
Disable HiDPI on BetterDisplay or BetterDisplay entirely removes artifacts immediately; they return once BetterDisplay is re-enabled.
macOS screen recording does not capture the corruption even while it is visible on the physical screen.

Environment:

• BetterDisplay version: 3.5.4
• macOS build: Sequoia 15.4.1
• Mac model: MacBook Pro 14-inch (M4 Pro)
• External display: Samsung G9 OLED 49 inch (5120 x 1440, mirror virtual screen enabled, HiDPI)

[waydabber]

Hmm. This seems to be some kind of macOS bug. If screen capture does not have it, then it's not in the framebuffer, the issue might be with the DCP or DCP firmware (this processes the framebuffer - video memory - and converts it to video signal). Issues like this can't be debugged really. Does this happen if you lower the refresh rate? If you are running the screen in high refresh rate, then the DCP might be at the edge of its pixel clock limit/processing power and might be failing somehow (just a theory).

[heungson]

The display is currently running at 240 Hz. The problem is that when I connect to a better display, the system gets locked at 240 Hz and doesn’t allow me to choose other refresh rate options like variable refresh rate (48–240 Hz), 120 Hz, or 60 Hz. This prevents me from trying a lower refresh rate like 60 Hz. As you know, since a virtual screen is being used, the actual content is shown at 60 Hz.

[waydabber]

Hmm. Do you have only one item in the Refresh Rate menu? What do you mean by "connect to a better display"? Do you mean virtual screen? If so, try enabling this obscure setting:

[heungson]

Hmm. Do you have only one item in the Refresh Rate menu? What do you mean by "connect to a better display"? Do you mean virtual screen? If so, try enabling this obscure setting:

'connect to better display' means with using BetterDisplay.

If I quit BetterDisplay, I can choose among these

but with BetterDisplay

even after

[waydabber]

The setting only affects the app's refresh rate menu, not the System Settings menu. Normally when you mirror a screen, you don't have the option to change the target display's refresh rate.