13" MBP 2020 - 4K + 5K display = ???

[KTamas]

I know that officially the (10th gen) 13" 2020 MBP supports two 4K displays or one 5K/6K displays. But what would happen if I'd try anyway and hook up a 4K and a 5K display, both through USB-C (two LG Ultrafines)?

Would the 5K one stay black? Would the internal display turn off? Would it let me use the 5K display but with a lower resolution? Would it work but it'd be unusably slow?

Thanks.

 

[UnBip]

13 + 4 + 5 = 22

2 + 2 = 4 => 4 the win!

More seriously, I don't think it can handle both at the same time based on Apple's description. Or Maybe will it be able to run the 5K at a lower 4K resolution?

 

[KTamas]

Guesses, I already have, I'm ideally looking for someone who actually attempted something like this in the past.

 

[Dhock_Holiday]

Your reaching the limit of the graphics overhead if that's your setup, I haven't tried it myself but I would imagine macOS would limit the resolution and probably drop down the refresh rate as well to compensate. It will likely struggle and you're going to see higher temps with added fan noise.

It would be best to look into an external GPU at that point or even return it for the 16 inch.

 

[joevt]

The LG UltraFine 5K uses two DisplayPort 1.2 signals. If it's connected first, then the 4K display won't work. If the 4K display is connected first then maybe the 5K will use a single DisplayPort connection for 4K resolution.

I think the Apple Pro Display XDR uses a single DisplayPort connection with the new Gen 11 graphics of the 10th gen CPU (HBR2 + DSC - I would like to see proof of that from AGDCDiagnose output). But it might have too many pixels to support another display.
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Another option might be a 5K display that uses a single DisplayPort 1.4 connection. But like the 6K, it might use too many pixels for a second display.