How to resolve macOS 15.4 HiDPI + HDR issues and frequent panic crashes on M4 Max with 5120x2160 monitor?

Good day everyone!

My MacBook with the M4 Max chip (64GB RAM) is connected directly via USB-C to an LG 45GX950 monitor (5120x2160 @ 165Hz, connected through the monitor’s Type-C port). After updating to macOS 15.4, I’ve been facing several major issues when using the 3840x1620 HiDPI resolution:

• The HDR toggle disappears completely once I select 3840x1620 HiDPI mode. It exists when I choose other resolution, ex. 3360x1418 or 5120x2160
• In macOS 15.3.1, this resolution worked fine with variable refresh rate (VRR) enabled. No HDR toggle though.
• But after upgrading to macOS 15.4, the system forcibly locks the refresh rate to 165Hz, and waking from sleep often causes the 3840x1620 HiDPI resolution to be lost. The refresh rate also gets locked to 100Hz for all available resolutions after waking from sleep.
• This issue doesn’t only affect the 3840x1620 HiDPI mode — even when selecting other resolutions (e.g., 3360x1418 with HDR enabled), waking from sleep can still result in HDR being completely disabled across all resolutions, with the refresh rate locked to 100Hz.
• The only temporary fixes are: reconnecting the display, restarting the monitor, or rebooting the Mac.
• If I don’t reboot and just lock + wake the screen again, the system often panics and crashes.

I’ve attached the panic report below.

From what I remember, macOS Sequoia 15.3.1 did not have this issue with the M4 Max waking from sleep.

On the other hand, my M1 Max MacBook (also 64GB RAM) using the same cable and the same monitor at 3840x1620 HiDPI works fine — no HDR toggle though, but variable refresh rate works, and it never crashes on wake. The software installed in these two Mac is exactly the same.

Has anyone else experienced this with macOS 15.4 and external displays on M4 Max? Any suggestions or workarounds?

[Re-Titled By Moderator]