BetterDisplay doesn’t pick up HDR capability when connected to DisplayPort KVM

[kael131]

Setup is an M4 Mac mini on 15.1, connected via USB-C to displayport to a UGreen Displayport KVM switch, to an Alienware 3423DW.

175Hz, HiDPI, that all works fine, but under the capabilities info screen, HDR is listed as ‘No’ no matter what I do. Dropping it down to 60Hz doesn’t have an effect. Disabling HiDPI shows no change. Restarted a few times, restarted the switch, but I can’t get it to appear.
The switch works fine with a Windows PC and I get the full bandwidth in the same way a direct connection would work.

The KVM does say on the box it supports 8k at 60Hz, so it should have enough bandwidth. HiDPI works fine at native 3440x1440 resolution at 175Hz.

I did try another display port cable for the monitor to KVM link, and saw no change. I’ve only got the one DisplayPort to USB-C cable, so I can’t switch that out, but connecting to the monitor directly with the same USB-C to DisplayPort cable does make HDR appear up to 70% resolution when HiDPI is used, so for whatever reason, the Mac or BetterDisplay can’t pick it up when the switch is used. 70% is fine and dandy; it makes text easier to read.

(above screenshot shows direct connection)

Is there anything I can do here to get it to work or try to force it? I had a brief look at the CLI page after I saw it mentioned in another discussion. Will the CLI features accomplish what I need?

[waydabber]

It might be an EDID or some kind of negotiation issue - some KVMs do meddle with things a lot. You can use CLI to list the available low level modes based on the parsed from the EDID and connection negotiations but if HDR is not showing up anywhere, it will just tell you that:

betterdisplaycli get -connectionModeListAll

[kael131]

It does seem to list HDR10 in 10 and 12 bit modes. Attached the truncated file. Kinda odd there isn't a 175Hz 10-bit at native res, but I could live with a 150Hz mode for HDR content. How do I add that?
connectionmodeslist.txt

[waydabber]

Since HDR resolutions seem to be available only with some awkward legacy NTSC refresh rates, you might have trouble getting this to work. You can do a low level mode switch to HDR but tone mapping won't work I am afraid. It seems like the KVM is messing with things indeed.

[waydabber]

I think the simplest approach is to try to export the display's EDID while it is natively and directly connected and then apply that EDID for the display when connected via KVM - maybe that will make things work (this will help if the KVM switch interferes with the EDID only).

[kael131]

Okay, so I disconnected from the KVM and directly connected. Performed a Retrieve EDID (got both an OS managed and Direct I2C retrieval and then exported the two sets of data. I then unplugged the monitor and switched back over to the KVM. I then went to Load Custom EDID, loaded the data by picking the OS managed export and then clicked Apply Custom EDID Now. That didn't have an effect. So I tried again with the Direct I2C file and it seems that might have worked? I appear to be locked at 100Hz however.

Did I follow the correct procedure?