Can't get M1 Pro to output 7680x2160 to Samsung 57

[rsteckler]

Been struggling for a few hours now trying to get my macbook to output 7680x2160 to my Samsung 57". I've tried virtual resolutions mirrored to the display, flexible scaling, over 8k framebuffer, etc.

No matter what I do, I can't get the monitor to show that it's receiving a 7680x2160 resolution. In fact, the only resolutions I can get the display to show on it's own information is 3840x1080 and 3840x2160.

This is using the macbook TB port with a usb->HDMI adapter
Here's what I've tried:

1. enabled 8k buffer
2. enabled flexible resolution scaling
3. tried changing detected native resolution to 7680x2160 (always shows up as 3840x2160, but can't be changed - just sticks there)
4. added custom 7680x2160 resolution, but it says not available
5. tried virtual mirror, but that doesn't change the actual monitor resolution to 32:9 so everything gets stretched
6. Tried 2 diff hdmi adapters: cable matter, white mac dongle
7. Tried CalDigit dock with displayport to HDMI adapter

It looks like other people have got this working and are trying to get 120hz - I would just be happy with 60hz!

[rsteckler]

Answering my own question after more research

It appears that the Mac M1 Pro allows 32:9 resolutions over displayport but not HDMI. This is unfortunate as the Samsung only has one displayport and that's being used by my PC.

Options for those who come here in the future are:

1. Get a new mac
2. Get a displayport switcher
3. Try this thread: HiDPI for 5120x1440 #56 (reply in thread)

[waydabber]

(note: repoened this as this might be useful for others - thank you! 😃)

[rsteckler]

For completeness, I was able to get 5120x1440 @ 120hz on the Samsung 57" using the Cable Matters TB4 to HDMI dongle. The process is:

1. Update the dongle using a windows computer with the new cable matters firmware. This makes the dongle report that it's a displayport adapter!
2. use EDID editor to modify the last CAE extension section to be 5120x1440. I tried 7680x2160, but it didn't work
3. Load that custom EDID profile into BD and boom.