External display issues HDMI, HDCP, EDID, No Audio

I suggest you search this forum for posts made by @Grant Bennet-Alder who is the forum expert on Macs & displays. @Grant has made many posts for assisting users with display related issues since the release of macOS 26.x Tahoe on Sept. 15, 2025.

macOS 26.x Tahoe has changed things a bit as higher quality cables are needed to better support communication with devices......especially with external displays. Generally, you need to use premium high quality cables which are less than 1 meter in length. For HDMI cables, you need to use:

Quoting @Grant Bennet-Alder in this post:

External Monitor Not Detected After macOS… - Apple Community

"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)

Here are a few posts by @Grant Bennet-Alder to get you started (in no particular order....there may be other posts by @Grant in each thread, these are the only links I had handy....there are actually much better & more detailed posts by @Grant):

Second external monitor not detected afte… - Apple Community

Multiple informative posts by @Grant in this single six page thread....covers a lot of areas to get you started:

External Monitor Not Detected After macOS…--- How macOS detects displays - Apple Community

External Monitor Not Detected After macOS…--- Display cable specifications - Apple Community

External Monitor Not Detected After macOS…--- Explanation why cables are the problem - Apple Community

External Monitor Not Detected After macOS…--- Another slightly different post about cable specifications - Apple Community

External Monitor Not Detected After macOS…--- One display per USB-C Port - Apple Community

External Monitor Not Detected After macOS…--- Display Link Information - Apple Community

External Monitor Not Detected After macOS…--- Compatibility - Apple Community

External Monitor Not Detected After macOS…--- Multiple Displays - Apple Community

Second external monitor not detected afte… - Apple Community

How do I connect two external monitors wi… - Apple Community

2020 MacBook Pro with external display wa…--- 2 Posts by @Grant - Apple Community

Edit: Here is an Apple forum search for @Grant's display related posts for macOS Tahoe:

Search - Grant Bennet-Alder Tahoe External Display -- Apple Community

YouAreNotAsGoodAsYouThink wrote:

# Mac doesn't folllow the standards of HDMI, so we are off to a bad start already.

There is nothing wrong with the USB-C (DisplayPort Alt Mode) standards that all modern Macs use.

# Mac forces a resolution (in our case, it sees that the device input can handle 4k, so it pushes that, even though at the other end it's 1080p, rather than let the user manually pick one even if you select the resolution in the list, it makes no difference, apparently, the mac knows best!!

If the display has a native resolution of 3840x2160 pixels, the "like 1920x1080" resolution that macOS emphasizes in the user interface will be Retina "like 1920x1080" mode, in which

• Text and objects are sized "as if" the display only had a resolution of 1920x1080 pixels
• Drawing is done in detail on a canvas with twice the nominal Displays Settings "resolution" in each direction – that is to say, at a 3840x2160 pixel level of detail on a 3840x2160 pixel canvas.
• The contents of this 3840x2160 pixel canvas are then mapped onto the actual 3840x2160 pixel screen.

In that scenario, there is no way that the Mac could send just a 1080p signal to the 4K monitor, while preserving the 4K level of detail.

If you display resolutions as a list, and tell the Mac to display all resolutions, it might offer two "1920x1080" choices, one of which will be "1920x1080 (low resolution)". If you choose that one, the Mac will draw in a coarser 1920x1080 pixel level of detail. Whether the Mac sends a 1080p signal to the 4K monitor and lets the monitor scale it up, or the Mac scales the 1080p signal up to 4K and sends a 4K signal to the 4K monitor, would be an implementation detail.

Apple, why is this so broken..????

You need to fix this!

This is a user-to-user forum. You are not addressing Apple here.

"External display issues HDMI, HDCP, EDID, No Audio: [...]It can take up to 10 unplugging and replugging attempts before I see the left channel appear and sometimes it just doesn't work at all, and I resort to a Windows PC, an older intel based Mac, or using a 3.5mm headphone connection to grab the audio. Apple, why is this so broken..???? You need to fix this!"

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Recommend Changes to Apple:

Do your Part: These are just user-to-user forums. You are NOT communicating with Apple here. We are just everyday apple users, like yourself. So, inform Apple of your feedback.  Apple wont get back to you directly, but the more feedback thy receive from its users, the more likely they will know what their customers prefer, and what to include in models to come. Apple will know nothing of your ideas, if you don't provide them to them.

1. Go Here: Feedback - MacBook Air - Apple
2. Select: "Performance" for the "Feedback Type"
3. Comment: that this does not meet your exceptions, and how you think things should be different. Include the URL of this thread.
4. Proceed from there as necessary

"External display issues HDMI, HDCP, EDID, No Audio: [...]It can take up to 10 unplugging and replugging attempts before I see the left channel appear and sometimes it just doesn't work at all, and I resort to a Windows PC, an older intel based Mac, or using a 3.5mm headphone connection to grab the audio. Apple, why is this so broken..???? You need to fix this!"

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External Monitors Not Working:

This could be anything from a hardware issue, to not meeting minimum system requirements, to a configuration profile, any of which don not permit access ti external display usage. Apple is proprietary, meaning they make their own minimum system requirements for their own devices and software. Note that Apple has a tendency of providing updates for 7 years, and then your device is no longer supported with updates.

Stream your Content:

If you want to see it all thought your network, then I recommend going for streaming services, such as Roku. You can stream it from you Apple Device. You need an Apple Account and a Roku account, and, of course, agree to Terms & Conditions.

How to Verify the Connection:

First off, see if the headphones are is even seen: 

1. Hold Down: the Option key
2. Click: the Apple menu
3. Choose: System Information or System Report
4. Select: Graphics/Displays from the list on the left
5. Look For: this devices