M4 Mac: sharp 4K HiDPI mode missing
Updated
Short answer
On M4 and M5 Macs, the sharp (HiDPI) frame macOS draws for an external display is limited to 6,720 pixels wide. A sharp “looks like 3840×2160” mode on a 4K monitor needs a 7,680-pixel frame, so it isn't available; the largest sharp size is looks like 3360×1890.
What changed
In HiDPI mode macOS draws everything at twice the “looks like” size, then scales the frame to the panel. On a 4K monitor, looks like 3840×2160 means drawing at 7680×4320. On M1, M2 and M3 Macs, tools that add display sizes could give you that mode. On M4 and M5 Macs the frame tops out at 6,720 pixels wide (2 × 3360), so those tools stop at looks like 3360×1890. Users reported it soon after the first M4 Macs shipped; developers traced the cause in 2026. Apple hasn't said whether it will change.
The default sizes are not affected. Looks like 1920×1080 (exact 2× on 4K) and 2560×1440 are still sharp.
Who notices
- People who used looks like 3840×2160 HiDPI on an earlier Mac for maximum space with sharp text.
- Screen recording and design work that needs a 3840×2160 point canvas with Retina detail.
The workaround
Create a virtual 3840×2160 HiDPI display (the limit doesn't apply to it), then mirror the real monitor to the virtual one. The monitor shows the virtual display's sharp frame. It costs some extra GPU work, and the mirror has to be set up again after sleep or reconnecting.
iKnowMyDisplay's Sharp 4K does this in one click, where your Mac supports it: it appears only on M4 and M5 Macs with a 4K display, restores the mirror after sleep, and removes it cleanly. Like every display change in the app, it undoes itself after 15 seconds unless you keep it.
Before buying a 4K monitor for an M4 or M5 Mac, the compatibility checker shows what to expect.