Second monitor stopped working with a new Mac Mini Apple M4 Pro

Asus – ASUS ProArt Display 5K PA27JCV

This is a 27" 5K (5120x2880) pixel monitor.

Unlike the Apple 27" 5K Studio Display – and just about all of the other 27" 5K monitors I've ever heard about – this monitor does not accept Thunderbolt input. It accepts:

• USB-C (DsplayPort Alt Mode)
• DisplayPort v1.4
• HDMI v2.1

Mac mini (2024) - Tech Specs - Apple Support

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Simultaneously supports up to three displays:

• Up to three displays: Three displays with up to 6K resolution at 60Hz over Thunderbolt or HDMI
• Up to two displays: One display with up to 6K resolution at 60Hz over Thunderbolt and one display with up to 8K resolution at 60Hz or 4K resolution at 240Hz over Thunderbolt or HDMI

Thunderbolt 5 digital video output

• Support for native DisplayPort 2.1 output over USB‑C

HDMI display video output

• Support for one display with up to 8K resolution at 60Hz or 4K resolution at 240Hz (M4 and M4 Pro)

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"Up to 8K resolution at 60 Hz [over HDMI]" implies that your M4 Pro Mac mini supports HDMI v2.1. If I remember correctly, HDMI v2.1 has something like three times the bandwidth of HDMI v2.0 (which has just barely enough for driving a 4K monitor at 60 Hz)."

For other recent Macs which do not have Thunderbolt v5 or DisplayPort v2.1, "Up to 6K at resolution at 60 Hz over Thunderbolt" generally translates into

• "Up to 4K resolution at 60 Hz over USB-C (DisplayPort Alt Mode)", or
• "Up to 6K resolution at 60 Hz over Thunderbolt"

Your monitor has a DisplayPort v1.4 input, so the question might then be, what DisplayPort v1.4 can handle, and/or what the Mac is willing to support when it sees a DisplayPort v1.4 connection.

CableMatters – DisplayPort v1.4 vs. HDMI v2.1: What You Need to Know

This article claims that DisplayPort v1.4 supports transmission modes that give it enough bandwidth to display 5K at up to 60 Hz.

I would assume that

• Many of the USB-C to DisplayPort adapters on the market do not support resolutions of 5K @ 60 Hz (e.g., due to using DisplayPort v1.2)
• Many of the USB-C to HDM adapters on the market do not support resolutions of 5K @ 60 Hz (e.g., due to using HDMI v1.4 or HDMI v2.0)

I don't know whether something like this might work:

https://www.amazon.com/DisplayPort-Maxonar-Thunderbolt-Adapter-Certified/dp/B08B3SB5VC

The description of this USB-C to DisplayPort cable explicitly mentions DisplayPort v1.4, and says that the cable supports 5K @ 60 Hz.

Or maybe any of the USB-C to HDMI v2.1 adapters here which claim to support 8K @ 60 Hz, and to be compatible with Macs.

The idea is that you don't want an adapter that

• Uses anything less than DisplayPort v1.4 on the computer side.
• Uses anything less than DisplayPort v1.4 or HDMI v2.1 on the monitor side.

There might be a lot of adapters that use DisplayPort v1.2 or HDMI v2.0 that will work fine with monitors that have more typical resolutions (1080p, 2.5K, 4K), but that just aren't able to handle the bandwidth needed to drive a 5K monitor.

If you're using a USB-C to USB-C cable to connect the Mac to a monitor, make sure that cable is a high-quality one that can carry the amount of data needed for 5K video. A certified Thunderbolt 4 cable might even be in order. My understanding is that modern versions of macOS do not like to see display transmission errors. If macOS sees any, it may cut resolution or even signal in response.

You could also try contacting Apple and Asus Support.