Since Apple has released macOS 14, aka Sonoma, I’m back with an update on whether they finally fixed the HDMI 2.1 issue with scaling and HDR that was prevalent with macOS 13, Ventura, and the M2 Pro or higher machines that have an HDMI 2.1 port.
I had previously talked about how macOS 13.0 had a bug in it, such that trying to enable higher scaled resolutions over HDMI 2.1 with the M2 Pro or higher Macs would eventually result in a green screen of death, which I tested on my LG C1 48″ TV as my monitor. This bug was fixed by version 13.2, but at the same time, a limitation was put in place where selecting a scaled resolution above 2432 x 1368 would no longer allow you to enable HDR and reach 120 Hz refresh rate.
Although the LG C1 is said to have slightly lower HDMI 2.1 port bandwidth than the newer LG C2, I actually did try the 42″ LG C2 TV more recently and ran into the same limitations.
In case you aren’t aware, macOS does scaled resolutions by rendering at twice the length and width of the chosen resolution, which is 4 times the pixels. Then it scales the UI to match the size of what you would see if you used the chosen resolution natively, so everything is much sharper and looks better.
Although logically it should down sample to the monitor’s native resolution before sending the signal, whatever macOS is doing seems to run into HDMI bandwidth limitations, so the combination of chosen resolution, refresh rate, and HDR cannot be used past a certain point.
So does macOS Sonoma improve the situation? Unfortunately, the answer is NO. Running macOS Sonoma, the same limits appear to be there, so I still cannot use my preferred scaled resolution of 2560 x 1440 with 120 Hz or VRR and still enable HDR. Because of this, I usually run at 2400 x 1350 resolution, which is 125% of 1080p, with VRR and HDR on, or at 2560 x 1440 with constant 100 Hz refresh rate and HDR.
As stated earlier, you could go up to 2432 x 1368 resolution with VRR and HDR, but that would be 1.266 repeating % of 1080p, so I figured the scaling would be slightly cleaner with 2400 x 1350.
It’s looking like we may never get this issue addressed with macOS, at least until new generation Apple Silicon and possibly even higher bandwidth HDMI ports are standard in computers and monitors or TVs.