Macbook Pro M5Pro missing resolutions and refresh rate on external monitor

Hello again andree. I don't know if you'll ever see this, but if you do, could you please give it a try?

I may have a theory about your 45GX950A being capped at 100 Hz.

I checked the manual of the 45GX950A. It only supports 5K2K at 165 Hz, 100 Hz and 60 Hz. There's no 120 Hz option. And we know that at least 120 Hz is required to enable 3860x1680 HiDPI layout.

Now, the question is why 165 Hz doesn't show up with the latest M5 Pro using TB5. The only difference between M5 Pro and M3 Pro is that the M5 Pro's TB5 connector supports DisplayPort 2.1, whereas TB4 on M3 Pro only supports DP 1.4 with DSC.

One possible explanation is that the downgraded DP 2.1 54 Gbps bandwidth version (commonly used by LG) may not be sufficient for 5K2K at 165 Hz without DSC, or there may be a DP2.1 issue with macOS, whatever.

However, since 5K2K at 165 Hz was previously confirmed to work with M3 Pro using DP 1.4 with DSC, what if you try disabling DP 2.1 in your 45GX950A's settings, fall back to DP 1.4 mode, and test again?

<< - DisplayPort over USB-C

- `LinkRateDescription = "8.1 Gbps (HBR3)"`. >>

HBR3 is the fastest s speed over USB-3, at 8.64 G bits/sec, just short of top USB 3 speed of 10 G bits/sec.

to run a Full 5K display at 10 bits color at 60 Hz without resorting to Display Stream Compression requires UHBR10 at 38.69 G bits/sec, just short of Top Full Thunderbolt-3/4 speed.

to run a 5K2K display at 10 bits color at up to 99 Hz without resorting to display Stream Compression requires UHBR10 at 38.69 G bits/sec, just short of Top Full Thunderbolt-3/4 speed.

it appears that forcing this data stream into a USB 3 port is what is limiting your resolutions.

--------

the best high performance adapter to DisplayPort that really can attain ThunderBolt-3/4 AND 5 speeds is this new CableMatters adapter:

USB-C to DisplayPort 2.1 Adapter

Product ID:  201386. Price:   $35.00 

https://www.cablematters.com/search.aspx?PageSize=20&PageNum=1&SearchTerm=201386

<< I'm using the supplied USB-C able and even tried a TB5 cable with no fix. >>

'Supplied' by whom?

Cables shipped in the box by most display-makers are guaranteed to have the correct connectors on the ends. Beyond that, they are often "lowest bidder" cables and are often inadequate for driving high-end displays at high resolutions.

Cables required for DisplayPort at near 4K and beyond should be high spec cables and are limited to ONE meter maximum at these data rates.

An ordinary Thunderbolt-5 cable, if operating at Thunderbolt speeds, is limited to 0.5 meters max for brand-X cables. There are a few highly engineered cables available that can run a little bit longer. Beyond that, you generally need an ACTVE Thunderbolt-5 cable, which starts at about US$100.

I ran into this exact problem last year when I bought a Mac Studio M4 Max to replace my old 2017 Intel iMac.

Incredibly, my old iMac can drive higher resolutions on my LG 40WP95C-W Ultrawide than this brand-new Mac Studio. It’s hard to believe that a machine nearly 10 years older handles display scaling better than one of Apple's most powerful current computers.

So far, the only workaround has been using the BetterDisplay app to create a virtual screen and associate it with the physical LG monitor. While it works, it’s far from an ideal native solution.

I’m honestly very disappointed. We are investing a lot of money into 'pro' hardware, only to find these limitations. It’s even more frustrating to hear that users with M5 chips are still facing the same issues. 

andreeinprogress wrote:

cedric1088 wrote:

Hello again andree. I don't know if you'll ever see this, but if you do, could you please give it a try?

I may have a theory about your 45GX950A being capped at 100 Hz.

I checked the manual of the 45GX950A. It only supports 5K2K at 165 Hz, 100 Hz and 60 Hz. There's no 120 Hz option. And we know that at least 120 Hz is required to enable 3860x1680 HiDPI layout.

Now, the question is why 165 Hz doesn't show up with the latest M5 Pro using TB5. The only difference between M5 Pro and M3 Pro is that the M5 Pro's TB5 connector supports DisplayPort 2.1, whereas TB4 on M3 Pro only supports DP 1.4 with DSC.

One possible explanation is that the downgraded DP 2.1 54 Gbps bandwidth version (commonly used by LG) may not be sufficient for 5K2K at 165 Hz without DSC, or there may be a DP2.1 issue with macOS, whatever.

However, since 5K2K at 165 Hz was previously confirmed to work with M3 Pro using DP 1.4 with DSC, what if you try disabling DP 2.1 in your 45GX950A's settings, fall back to DP 1.4 mode, and test again?

• Hey, thanks! Yes I'm reading all messages here (and AFAIK someone from Apple should be too).

Thanks for the suggestion but I already tried that, without success. (really tried pretty much every combination on phone with support).

on TB5, with every cable I tried, 2.1 option is not even available, so it's 1.4

• on direct DP with a proper cable both 2.1 and 1.4 are available. the only differences in setting it to 1.4 are that it enables HDR (only on low resolutions), but also caps at 100Hz

Thank you very much for the update.

I strongly believe there is a serious regression with how the M5 Pro handles DSC under DP 1.4 mode.

I don't know if DSC is required to run 5K2K at 100Hz, but it's definitely required for 165Hz. I see two possibilities.

1. If DSC is required for 100Hz, M5 Pro's DSC limit might have been lowered from 165Hz to 100-120Hz range.
2. If DSC is not required for 100Hz, M5 Pro's DSC might not work at all for whatever reason.

Hopefully it works with 120Hz, but 45GX950A doesn't support 120Hz, we need someone with Dell U4025QW to do a test.

It's tied to M5 Pro, not the port, because some users have reported that it works on the M4 Pro, which has the same Thunderbolt 5 port with DP 2.1.

The remaining question is whether it works on the base M5, which doesn't support DP 2.1 at all. If its DSC feature is broken, its usability is gravely compromised.

There are two regressions here. The first is the one you mentioned: it affects starting from the M4 series. For example, the M4 Pro cannot achieve `3840x1620 HiDPI 165Hz` with HDR enabled, but it *can* achieve `3840x1620 HiDPI 165Hz` without HDR at 10-bit color, full RGB. whereas the M3 Pro supports this with HDR without any problem. This applies to all ports and connectivity methods, including native HDMI, USB-C/Thunderbolt, and USB-C/Thunderbolt to Dock/DP.

The M5 series’ native HDMI port shows the same behavior as the M4 series. BUTTTTT the M5 series has a separate regression on the USB-C/Thunderbolt ports, where you get even fewer options no matter what kind of port/adapter/dock you try.

This is a User-to-User Support Community, and Readers are other Users like you.

if you want to get your issue to an Apple employee to consider, you can use the product feedback pages, and report type "Bug Report". These reports are noted, but not tracked to resolution.

You can include a link to this discussion.

Product Feedback - Apple

if you want to pursue this to a formal, tracked Bug Report, you need to contact Apple Telephone Support

The telephone support people are more likely to work with you. They will insist that you go through the motions to eliminate software issues. But when they get to the end of their list, Do NOT allow them to tell your it’s fine or there is nothing more they can do for you!

You should insist on having your problem escalated to a Specialist. Specialists are more likely to actually read your panic or other reports. If still no resolution, ask them to start a formal, tracked Bug Report on your behalf. If they think this might be a Hardware problem they can DIRECT an Apple service provider to swap things (likely mainboard) for a new one.

Apple support does appreciate what we do as Volunteers here on the forums. They can and should read what has already been posted. Be sure to tell them where they can read it. But they do NOT take our conclusions at face value -- they have their own more rigorous procedures they follow.

You MUST have a Trusted backup before submitting your Mac for service. if the mainboard is swapped out, the boot drive will be swapped out as well, and you will not get your files back.

Support

I agree with many posters here that these M5 Macs, and possibly some M4 Macs as well, seem to have issues that go well beyond the limited input speeds on certain displays or wrong cables. They have issues with not being able to set up fast enough connections. Most of this looks to me like a problem in the Mac, and I expect there will eventually be a software solution.

Be sure you use the Apple Product fFeedback pages or contact telephone support (Both references above) and let them know, so that the stack of complaints gets tall enough to tip over and they fix this mess.

I did more research. Sorry, I just don't want to give up. xD

The situation is worse than I thought. As someone mentioned, there are multiple regressions here.

1. HiDPI Mode 3840x1680 is only enabled at 120Hz+ since M4. This one has an explanation.
2. But in your case, your display is capable of doing 3840x1680@165Hz, but for whatever reason, the TB5/USB-C/DP-ALT connector paired with the latest M5 Pro is capped at 100Hz. Since it's below 120Hz, no 3840x1680.

I mean, the 2nd issue is really serious for a Pro machine. Apple really needs to fix it as soon as possible.

that LG 45GX950A-B appears to be 5120 by 2160 (5K2K display capable of 10 bits/color and refresh rates from 48 to 165 Hz.

connectivity includes:

2x HDMI 2.1

2x DisplayPort 2.1 (UHBR 13.5 w Display Stream Compression (DSC)

USB-C 3.1. top speed would be 10 G bits/sec, called out as a data transmission port

Those specs and others available do not say that display is capable of direct Thunderbolt connection.

¿Are you using an adapter or adapter/cable? which one?