5120 x 1440 on a 2019 Macbook Pro 16''

[my_chemical_mac]

I've got a 16" 2019 MacBook Pro with AMD Radeon Pro 5300M GPU. I've got it connected to the Samsung Neo G9 (5120 x 1440 resolution, 240 Hz) via a USB-C to HDMI cable (this one), but I am limited to 3840 x 1080 resolution. How can I achieve the full 5120 x 1440 resolution here? I don't care if I don't get the full 240 Hz refresh rate, but at least 60 would be nice. It seems like this should be possible. Am I using an insufficient cable? Do I need an external GPU or something else?

From the MacBook's Technical Specifications:

• Up to two displays with 6016‑by‑3384 resolution at 60Hz at over a billion colors

Additional Notes:

• The computer is also connected to a 4k 60 Hz monitor via this cable, and that is working properly.
• The 1 DisplayPort input on the Neo G9 is already occupied by a gaming PC, so I would like to use HDMI here if possible.
• Operating in clamshell mode (internal display not in use)

 

[omnimax]

Don't think you can achieve 5k/60 over HDMI (at least I couldn't and others as well from what I've read on forums) on my non-Neo G9. That MBP model doesn't have HDMI2.0 native support so I think you need an active HDMI2.0 converter (similar to what apple sells) because native output won't be HDMI2.0 compatible so you're probably only getting DP alt mode which I think tops out at v1.2 (IIRC).

The 6k comment refers to using TBT3 so the only way to do full capability out of the G9 is with DP1.4.