Hello Apple engineers, I’m trying to determine whether what I’m seeing is expected behavior or a software issue with the new M5 Pro platform. System MacBook Pro (M5 Pro) Latest macOS Beta External 5K 165Hz monitor connected via DisplayPort Refresh rate correctly detected as 165Hz What I observe The display itself is clearly running at 165Hz. For example: Mouse cursor movement is extremely smooth. Dragging the desktop by holding an empty area is also perfectly smooth. However: Moving application windows feels much closer to 60Hz. Scrolling in Safari, Chrome and other applications also appears to run at a much lower frame rate than the display refresh rate. Mission Control animations sometimes show similar micro-stutters. This makes the cursor and desktop movement noticeably smoother than normal window animations. ⸻ Troubleshooting already performed Different DisplayPort cables Different timing configurations Different resolutions / HiDPI modes DSC enabled and disabled Refresh rate confirmed at 165Hz Same behavior across multiple applications The issue appears unrelated to the monitor itself because the cursor is clearly rendered at the full refresh rate. ⸻ Additional observation Interestingly, I previously used another external 4K 144Hz HDR monitor and did not notice this behavior. I also found another M5 Pro user reporting nearly the same issue: external 165Hz display smooth cursor window dragging jitter / micro-stuttering At the same time, I haven’t found similar reports from M4 Pro or the base M5 running the same monitor. ⸻ My question Could this be related to the new M5 Pro display pipeline (WindowServer, Display Engine, or DCP)? Is there any known issue regarding high-refresh-rate external displays on the M5 Pro platform? Or is there additional diagnostic logging (WindowServer, DCP, Metal, etc.) that would help identify whether frames are actually being presented at the display refresh rate? I’d be happy to provide: sysdiagnose WindowServer logs Screen recordings Display timing information IORegistry dumps if they would be helpful. Thank you!

On the new M5 Pro platform running macOS, UI animations (window dragging, Safari/Chrome scrolling, Mission Control) on an external 5K 165Hz display appear to render at a much lower frame rate (~60Hz) or exhibit severe micro-stuttering. However, the mouse cursor and desktop wallpaper dragging remain perfectly fluid at 165Hz, indicating a potential issue in the WindowServer compositor or display pipeline rather than the physical link. Environment • Hardware: MacBook Pro (M5 Pro) • OS: macOS 27.0 beta 3 (26A5378j) • External Display: 5K 165Hz monitor connected via DisplayPort (DSC confirmed via IORegistry). System Settings correctly detects and selects 165Hz. Expected Behavior All UI elements, including window movement, application scrolling, and system animations, should render smoothly at the native 165Hz refresh rate matching the hardware capabilities. Actual Behavior The display output appears split between two different refresh rates: 1. Full 165Hz: The hardware mouse cursor and desktop dragging (empty area selection) are perfectly smooth. 2. ~60Hz / Jitter: Application windows (Finder, Safari, Chrome) stutter heavily when dragged or scrolled. Mission Control animations suffer from micro-stutters. Note: This specific combination suggests the Hardware Cursor layer is running at full rate, but the WindowServer compositor layer is throttled or dropping frames. Troubleshooting Performed (No Change) • Verified with multiple certified DisplayPort cables. • Tested across various resolutions (Scaled/HiDPI modes) and toggling DSC. • Regression Check: This issue did not occur on a 4K 144Hz HDR monitor previously, and initial community feedback shows other M5 Pro users experiencing this specific 165Hz window-dragging jitter, while M4 Pro / base M5 users on the same macOS beta do not seem impacted. Questions & Diagnostics 1. Is this a known regression related to the new M5 Pro display engine / Display Coprocessor (DCP) pipeline handling 5K high-refresh-rate timings? 2. Are there specific defaults write commands, Quartz Debug profiles, or custom logging arguments (WindowServer, DCP, or Metal) we can enable to capture frame presentation metrics? I have captured a sysdiagnose, IORegistry dump, and high-frame-rate screen recordings, and am ready to attach them as soon as this feedback is processed. Case / Feedback Reference Feedback ID: FB23616959 (Captured after the system format)