Macbook Pro M5Pro missing resolutions and refresh rate on external monitor

<< I have tried with: a TB5 cable (which is compatible), a USB4 cable (which is compatible), a USB3.1 cable. All the same. >>

and I have said, "None of those direct connections should be working AT ALL"

according ti the manufacturers specs and third-party reference sites, that display does not have a Thunderbolt input port, and connection to the USB-C port might not work at all.

If we pretend for a moment that the display's USB-C port actually will accept data, it will be very limited in highest resolutions and refresh can be displayed.

¿Is that similar to what you are complaining about?

¿Is the link you posted for the EXACT model number you are running? LG has a half dozen or more all called UltraWide.

¿is you display actually this 40WP95C-W ?

<<. Direct HDMI (to the HDMI port) works without issues, that resolution is available, and 165Hz too.

However, HDMI to any USB port via a USBC-HDMI cable has the same issue >>

An adapter from USB-C to HDMI is limited by BOTH USB-C top speed AND HDMI 'quantization' -- that HDMI speeds are a step function that only uses certain speeds. The result is that you can not attain highest data rates over USB-C to HDMI adapter.

when you do this, you must rely extremely strongly on Display Stream Compression, which at higher demands starts to become "lossy" and your picture would become 'smeary'. It is plausible that later Apple software does not allow that.

DIRECT HDMI has a faster top data rate than DisplayPort connection for that display.

You should only need a USB connection for changing LG display settings, a 'once in a while' operation. Once set up, steady state display operation does not involve the LG monitor software at all.

My recommendation would be to use Direct HDMI for data.

Same issue here. Regardless what's the actual display specifications, the reality is that the M5 Pro currently has a significant regression in supported resolutions and display modes compared to the M4 Pro and M3 Pro — I kept my previous-gens and was able to verify this. Apple should fix this instead of forcing people to buy TB5 dock.

C’mon folks. Doesn’t anyone do a Search before they post? This issue has been discussed here before. There was a long thread on here about how the M4-based systems didn’t support a 3840x1620 HiDPI “ideal” resolution anymore with 5K/5K2K external displays; most often with LG’s monitors. M3-based systems supported that resolution just fine. This is not a new issue with M5-based Macs; although reading through all the replies to this post, there may be an even further regression with the M5s in terms of higher refresh rate support (i.e. 165 Hz) than even the M4s. Apple seems to be heading in the wrong direction …

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.

The settings screens you are showing are for the external display AND the built-in display locked together at a computed 'compromise' resolution in Mirrored mode. The settings are trying to apply to BOTH displays.

¿What happens when you change settings for the Acer 4K display alone, not Mirrored?

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

LG 45GX950A-B

M3 Ultra Mac Studio and M4 Max MacBook Pro could both drive this at 165Hz using the LG provided USB-C cable, and now my M5 Max MacBook Pro can only go up to 100Hz. It's not a cable problem, it's a M5 problem.

LG 38WN95C-W appears to be a 3840 by 1600 display at 10 bits/color (HDR) capable of referesh rates up to 144Hz. like a 4K display with some missing off the bottom.

interfaces include:

• Thunderbolt-3 -- IF fastest speed is supported, it can support UHBR10 at 38.69 G bits/sec up to 144 Hz without Display Stream Compression

• DisplayPort 1.4 -- this input is limited to HBR3 at 25.92 G bits/sec, effective data rate 4K at 120 Hz without Display Stream compression.

• 2x HDMI 2.0 -- this input is limited to a top speed of only 14.4 G bits/sec data rate, 4K at 55 Hz without Display stream compression

You could also consider as a work-around, using a USB to HDMI adapter AND an HDMI cable (TWO cable connection) to get the desired resolution at refresh rate.

Yes, no problem. I will make sure to raise the issue at the store.

By the way, last night (almost no sleep, lol), I did some research and found a very detailed analysis about this issue.

https://smcleod.net/2026/03/new-apple-silicon-m4-m5-hidpi-limitation-on-4k-external-displays/

It's worth a read.

If I'm not mistaken, it's a software issue. It shouldn't be a difficult fix, but it seems they just don't want to address it.

Dylanpict -

Please use Apple Product feedback page to post what you wrote above as a Bug report:

Product Feedback - Apple