The issue of 3840x1080 HiDPI being disabled in a Thunderbolt 4 environment.

[skyprawngo]

Hello, I’d like to ask about an issue I’m experiencing with HiDPI not functioning in a Thunderbolt 4 environment on my MacBook M4.

Here are the details of my setup, listed in the order the monitor signal passes through:
• MacBook M4 (M4 chip)
• Thunderbolt 5 (C-to-C) cable
• OWC Thunderbolt 5 multi-dock
• C-to-HDMI cable (HDMI 2.1 / 8K 60Hz, 48Gbps)
• Samsung G9 monitor (LS49CG934SKXKR, 5120x1440, 240Hz)

I don’t aim to enable HiDPI for the monitor’s maximum resolution. I simply want to use a single Thunderbolt 5 cable connected to the MacBook to achieve 3840x1080 at HiDPI with a refresh rate of 120Hz.

When I connect the MacBook and monitor via HDMI-to-HDMI, I can confirm that 3840x1080 HiDPI works correctly. Given the signal bandwidth of all the devices in my setup, I believe 3840x1080 HiDPI at 120Hz should be feasible.

However, after setting the resolution to 3840x1080 and clicking the HiDPI option, the resolution drops to 3072x864. I’d like to know why this happens.

Additionally, if I purchase the Pro model, would I be able to use 3840x1080 HiDPI at 120Hz?