Bypass Apple HDR restriction at high refresh rates/large screen sizes

[mustdobetter]

BetterDisplay has allowed me to pair my LG C2 42" with my MacBook Pro M1 Max, giving me 120hz via the Cable Matters USB-C to HDMI adapter. I'm loving this setup, and so glad there's a workaround in place to give me a proper monitor-like experience with this external display (TV).

The only limitation that I face is the lack of HDR support with 4k resolution @ 120hz. I've done some digging and the following reddit discussion contains a comment from Apple on the matter. This essential states that they've deliberately disabled HDR for larger screen sizes/higher refresh rates on external displays on macOS 14.1+:

Hello. Unfortunately, there is a frontend bandwidth limitation that prevents us from reliably supporting HDR at high refresh rates beyond a certain screen size, so we have had to gate the feature slightly more conservatively than in earlier builds of the OS.

I wonder if there's a way to bypass this restriction, as has been done with the refresh rate?

[waydabber]

No, this limitation is not about the connection but the framebuffer size an framebuffer pixel clock. Apple can limit this in the DCP firmware. There is no way around it. Not sure why Apple did it especially as it worked just fine for 2+ years. Interestingly same limitation applied to M2 initially while (probably due to fix the M2 green screen of death bug) while M1 was unlimited (which was awkward as the older chip seemingly did better than the new one) - but when they limited M1 they removed this limit from the M2 and fixed the green death bug. A more transparent explanation would be helpful from Apple. :)

[mustdobetter]

Thanks for the detailed explanation, as ever @waydabber. Not the answer I was hoping for, though ;) So essentially I can choose between 60hz and HDR or 120hz and no HDR. Or the third option, which presumably Apple would prefer: upgrade to M2 or M3 - ho hum.

[waydabber]

120Hz HDR should work up to 2432x1368 HiDPI (with 4K output - weird cut-off resolution from Apple there). Limit is lower for 144Hz and higher for 100Hz. I assume you wanted to use 2560x1440 so this might be an acceptable tradeoff.

[mustdobetter]

You assume, right. Thank you again - this is indeed a better tradeoff than lowering the refresh rate 👍

[dbacks2196]

Thanks so much, @waydabber, and sorry you're facing that issue, @mustdobetter. I can confirm that I have the same problem with an M3 Max, and I can't figure out a way to get HiDPI resolutions > 2432x1368, refresh rates > 60Hz, and HDR to work simultaneously. I submitted a report through Feedback Assistant asking if there is or will be an option to re-enable it from the command line in the recovery partition (or whatever they're calling that for Apple silicon Macs). It seems like getting enough people to complain to Apple about it is the only way, since it's not something that can be fixed with any third-party tools like BetterDisplay.

[devrimerduman]

I have mbpr 2018 and cable matter adapter and benq ex3210u monitor. and I cannot get 4k 120hz.....

[JESSUSA809]

Bonjour sava j’ai Apple taux rafraîchissement hz optimisation de optimal optimum maximum maximal garantie contre des défaut usure charge rapidement bonne journée fonctionne bien en vert bonne journée développeur iOS

[waydabber]

I just want to note here that on some models you can bypass the restrictions by holding hold SHIFT while opening the Refresh Rate menu in BetterDisplay - this way you can use a low-level mode switch to proper 120Hz or even a 120Hz VRR mode with high resolution modes - so you can trick macOS into a HDR 120Hz mode. On some models this will cause a green screen of death though (that's why Apple disabled this the first place, but the limitation affects Mac models that otherwise have no issue, probably for the sake of consistency).

So first switch to 60Hz HDR with a higher scaled resolution, then do SHIFT + Refresh Rate. Low level mode switch options have that wave symbol in front of them.

This is for example at a scaled resolution of 3072x1728 HiDPI in HDR with on an LG C5:

[martian099]

Thanks for the answers, it works but the setting won't stick. Like if the display sleeps and wakes up again, it's in SDR not in HDR mode. Any idea how to make it stick? I even purchased the pro version to use the configuration protection, but it doesn't do anything. Still goes back to SDR after display sleeps. Also tried to turn on Reinitialize this display on wake/unlock, same issue. Is there a way to add a feature and make this 120hz HDR setting stick in BetterDisplay? @waydabber

[waydabber]

Yes, this does not stick indeed. You can however create a simple keyboard shortcut or even add a script (or macOS Shortcuts shortcut with the proper set of actions) that you can run (even on wake) that sets the low refresh rate, enables HDR and then switches to the proper connection mode with the high refresh rate. It's a sequence of settings that must take place and the Configuration Protection does not cover this hack.

[Gusto2296]

I'm trying to make that shortcut, but it needs to use shift + 120hz (variable). not just click on the 120hz (variable) option. So it doesn't work. There's any way to make right that shortcut?

[waydabber]

Hi,

take a look at this - you need to do something similar (aside from the HDR stuff): #4986 (comment)

In Shortcuts you can create a Shell Script action and use the direct connection mode change that way using the mode ID.