I can't connect my MacBook Pro with P2422H dell

That Dell P2422H is a 1920 by 1080 display at 8 Bits/color (6 bits + FRC)

Display Interfaces include:

• DisplayPort 1.2
• Analog VGA
• HDMI 1.4

the USB-A port is a convenience data-only port, and can not be used for display data

if you have an Apple-silicon M-series Mac, the highest data rate is provided by the DIRECT HDMI Port. Adapters to HDMI are not recommended in most cases.

To use its HDMI Port, You MUST use high-speed DATA cables, not the ones 'found' behind your TV set.

HDMI cables you want for HDMI-only Displays (higher resolutions than 720p TV sets) are marked as Certified with an anti-counterfeiting tag and are labeled:

"PREMIUM High Speed HDMI cable" or that + "with Ethernet" (up to 4K at 30Hz) --OR--

“ULTRA High Speed HDMI cable" or that + "48G" (supports higher resolutions and backward-compatible)

Cables with No Certification tags are good for your standard 720p TV set, and not much more.

HDMI was invented for HD TV sets. it works great at its original resolution of 720i or 720p. At higher resolutions, it quickly develops issues that are complex to solve, and the cables and adapters required to solve are NOT intuitive.

DisplayPort:

An adapter or adapter/cable is limited to ONE meter maximum. Longer cables can cause signal losses that cause data errors, and the Mac will NOT connect if errors are occurring.

As a result of this thread, I went back to my original thread and found a reply that I had missed from Grant Bennet-Alder, who recommended deleting some .plist files. I'm delighted to say that this has now resolved my issue!

I'm copying his response below. Please note that you must delete the relevant .plist files in both the Library File on Macintosh HD and in your User Library (which you may need to reveal in the Finder by going to "Show View Options"). The ~/Library/Preferences/ByHost/com.apple.windowserver.<UUID>.plist file was the culprit for me.

Grant Bennet-Alder

Aug 25, 2025 01:02 PM in response to JC_JC

if you have met the other recommendations such as cable lengths:

For MacOS 12 Monetary nd some later versions, some users got relief by deleting two preferences files, then Restarting:

Library/Preferences/com.apple.windowserver

~/Library/Preferences/com.apple.windowserver.<UUID>.plist -OR-

~/Library/Preferences/ByHost/com.apple.windowserver.<UUID>.plist

-- where [~] tilde is an active abbreviation for "current user"

-- and <UUID> is a string of hexadecimal numbers unique to your system, grouped as 8-4-4-4-8 hexadecimal digits

Restart REQUIRED after these deletions.

If you have an M4-family MacBook Pro that has both USB-C / Thunderbolt ports and a HDMI port, then either

• a HDMI to HDMI cable, or
• a USB-C to DisplayPort adapter cable

should work.

You may want to check that the input selection on the display is set to match whichever input you are using. Sometimes displays will switch automatically to the input that is providing a signal – and sometimes not.

that sounds like the right kind of cable. How long is it?

The Mac does not rely on Windows-like side-loaded "Drivers" which are actually packages of resolutions and settings for a specific display. Instead, it goes straight to the immutable source -- it asks the display itself.

To get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display. "No signal detected" is generated by the DISPLAY, not by the Mac.

This query is only sent at certain times:

• at startup

• at wake from sleep — so momentarily sleeping and waking your Mac may work

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• hold the Option key while you click on the (Detect Display) button that will appear in Displays preferences (from another display)

so try doing some of those things and see if the display comes alive.

The Mac is very fussy about those cables. If any transmit errors occur, the dimply will be blanked. that is why form most purposes up to about 4K at 60 Hz, ONE meter cables are the longest generally recommended.

For higher resolutions, some cases require 0.5 meter cables.

For displays up to 4K at 60 Hz, adapters or adapter/cables from USB-C to DisplayPort generally suffice, provided cables are under ONE meter.

For resolutions over 4K at 60 Hz at 10 bits/color, a Dock may be required. This is because you need convert full-speed ThunderBolt -3 or -4 to high speed DisplayPort. At those speeds, that also requires more power, and the cables may be limited to 0.5 meters.

try using display port using a dock

Re: “can use a workaround involving screen mirroring to an iPad, which demonstrates that it is not a hardware or cable issue.”

Sidecar uses a software-based method which is different from (and not as good as) hardware-supported video output. So if it is working, that does not demonstrate what you think it does.

It's not supposed to be difficult. Perhaps the following is relevant.

Use the correct cable for your display. Check the documentation that came with your display and make sure you have the correct cable to connect your display.

Use an external display with your MacBook Pro - Apple Support

Maybe it's time to try a ONE meter cable that meets those specs.

Hi! I've got a similar problem to you (described and discussed here: MacBook Pro M4 Pro HDMI External Display … - Apple Community). I still haven't resolved it yet either, but I can use a workaround involving screen mirroring to an iPad, which demonstrates that it is not a hardware or cable issue.