HiDPI mode not restored after Pro license reactivation on non-standard resolution display (400x1280)

[heywook]

Environment

• macOS on Apple Silicon
• BetterDisplay v4.2.3 (Pro license active)
• Display: ZL400X1280 — native panel resolution 400×1280 (vertical bar display)
• Connected via USB-C, rotated 90°
• Target mode: 640×200 scaling:on (HiDPI, framebuffer 1280×400, 1:1 pixel mapping)

Problem

The display was working perfectly at 640×200 scaling:on (HiDPI) with BetterDisplay
Pro. After the Pro license expired and was later reactivated, the HiDPI mode no
longer applies. The display is stuck at 600×800 scaling:off.

What I've verified

Using Swift CGDisplayCopyAllDisplayModes with
kCGDisplayShowDuplicateLowResolutionModes:

• Mode 640×200 px=1280×400 HiDPI exists but has flags=0x2000001 (valid +
  mirrorable, no safe bit)
• Mode 540×960 px=1080×1920 HiDPI has flags=0x3 (valid + safe) — this one switches
  fine via BetterDisplay GUI
• Only 600×800 has usable=True

The display's EDID declares native resolution as 1920×1080, causing macOS to
classify the 400×1280 mode as usable=False.

What I've tried

1. EDID override plist with scale-resolutions — modes appear in list but remain
   usable=False
2. displayplacer CLI — exits 0 but no actual mode change
3. CoreGraphics CGDisplaySetDisplayMode — err=1001 (kCGErrorRangeCheck)
4. Private API CGSConfigureDisplayMode — ConfigureDisplayMode succeeds,
   CGCompleteDisplayConfiguration returns err=1001
5. CGDisplayCapture + SetDisplayMode — still err=1001
6. CGVirtualDisplay + mirroring — resolution changes but panel scaler produces
   letterboxing
7. BetterDisplay settings: "Edit native panel pixel resolution" → 400×1280, "Enable
   flexible scaling" — no effect after reboot
8. Full uninstall + reinstall (brew uninstall, defaults delete, removed
   override plists, fresh brew install, re-entered Pro license, reconfigured native
   panel resolution + flexible scaling) — still no change after reboot

Conclusion

It appears that Apple Silicon DCP blocks mode switching for any mode without the
safe bit (flags lacking 0x2), and BetterDisplay Pro's usable flag modification is
not taking effect even with an active license after reinstall.

Before the license expiry, this exact setup worked — BetterDisplay was able to make
640×200 HiDPI usable.

Question

Is there a known issue with Pro license reactivation not restoring the usable flag
override? Is there a specific setting or reset procedure I'm missing to re-enable
HiDPI for non-standard resolution displays?

Any guidance would be appreciated. Thank you.

[waydabber]

This should not depend on Pro availability, so I am not exactly sure what happened. But it is surprising that such a resolution worked.

I recommend doing a low level mode switch. While the app is running, enter this in Terminal:

/Applications/BetterDisplay.app/Contents/MacOS/BetterDisplay get -n=ZL400X1280 -connectionModeListAll

Then look for the preferred timing+color mode combo and copy its long mode id number and enter the following:

/Applications/BetterDisplay.app/Contents/MacOS/BetterDisplay set -n=ZL400X1280 -connectionMode=xxx

where xxx is the long mode identifier number you copied.

This operation should hard-switch to the appropriate mode, but the framebuffer will be left in its last canonical display mode size (make sure you select one that is larger than the desired timing's native resolution), so whatever content you want to show on the screen will have to be cropped. But this is usually fine for special displays or led strips as you should be able to control the content placement properly by other means.

Let me know if this works.