I'm not at home to try anything, but this is what AI is currently suggesting:
My thought process
You've done an excellent job isolating the problem. Because the card works on other devices, another card fails on this Mac, and both the built-in slot and an external USB card reader exhibit the exact same behavior, we can draw a solid conclusion:
Your hardware is detecting the card, but macOS's background disk-mounting system (or a security permission) is hung or blocking the volume from loading.
Since Disk Utility sees the physical drive (greyed out) but fails when you click "Mount", you don't need any sketchy third-party software. The solution lies in resetting macOS's disk mounting services or security permissions.
Here are the step-by-step fixes, ordered from simplest to most thorough.
Step 1: Check "Allow Accessories to Connect"
On recent macOS versions (Ventura, Sonoma, Sequoia), Apple added a security feature for MacBooks that blocks USB/SD card data lines until approved. Sometimes this setting glitches and allows the Mac to "see" the hardware in Disk Utility while blocking the actual data volume from mounting.
- Open System Settings > Privacy & Security.
- Scroll down to the Security section.
- Look for "Allow accessories to connect".
- Change it to "Automatically When Unlocked" (or if it's already set to that, switch it to "Ask Every Time", unplug the card, plug it back in, and click "Allow" on the prompt).
Step 2: Restart the Disk Arbitration Daemon (
macOS uses a hidden background process called diskarbitrationd to manage disk mounts. If this process gets stuck in a loop, no external storage (SD cards, USB drives) will mount—even across restarts if the saved system state restores it.
- Unplug the SD card.
- Open Terminal (press Cmd + Space, type Terminal, hit Enter).
- Type the following command and press Enter:
bash
sudo killall diskarbitrationd<br>
- Enter your Mac admin password when prompted (the characters won't show as you type).
- (macOS automatically restarts this service in under a second).
- Also run these two commands to clear any stuck file system background helpers:
bash
sudo pkill -f fsck<br> sudo pkill -f mount<br>
- Plug your SD card back in and check if it mounts.
Step 3: Try Force-Mounting via Terminal
Using the command line bypasses the Finder/Disk Utility interface and will give us a specific error code if it fails.
- Insert your SD card.
- Open Terminal and run:
bash
diskutil list<br>
- Look through the output for your SD card (it will usually be near the bottom, named something like /dev/disk2 or /dev/disk3, with a partition like disk2s1 or disk3s1).
- Run the mount command using your card's specific partition identifier:
bash
diskutil mount /dev/disk2s1<br>
(Replace <em>disk2s1</em>
with your actual partition identifier). 5. If it fails, try mounting in Read-Only mode:
bash
diskutil mount readOnly /dev/disk2s1<br>
If Terminal gives you an error message (like "Resource busy" or "Permission denied"), take note of the wording—it pinpoints exactly what is holding the drive hostage.
Step 4: Boot into Safe Mode (Clears System Caches & Resets Daemons)
Booting in Safe Mode runs a directory check on your Mac's internal drive, clears system caches, and prevents non-essential background processes from launching.
- Apple Silicon (M1/M2/M3/M4): Shut down your Mac completely. Press and hold the Power button until "Loading startup options" appears. Select your main hard drive (Macintosh HD), hold the Shift key, and click "Continue in Safe Mode".
- Intel Mac: Shut down. Turn it on and immediately press and hold the Shift key until the login screen appears.
Once logged into Safe Mode, test the SD card. If it mounts in Safe Mode, restart your Mac normally—the system cache reset often fixes the issue permanently for normal boots.
Step 5: Test in macOS Recovery Mode (The Ultimate Diagnostic)
If none of the above works, test whether the card mounts inside macOS Recovery. This completely rules out any software glitch in your main user environment:
- Shut down your Mac.
- Apple Silicon: Press and hold the Power button until options appear, select Options, and click Continue.
(Intel: Hold <em>Cmd + R</em> while powering on).
- Once in Recovery Mode, open Disk Utility from the menu.
- Plug in the SD card and see if you can click Mount.
- If it mounts in Recovery Mode: The hardware is 100% fine. The issue on your main system is being caused by a background app, system extension, antivirus, or VPN installed on your Mac.
- If it refuses to mount even in Recovery Mode across multiple ports and readers: The Mac's system controller firmware (SMC/NVRAM state on Intel, or system management controller on Apple Silicon) needs a hardware reset.
Summary Checklist:
Try Step 1 and Step 2 first—restarting diskarbitrationd and checking accessory permissions solves this exact issue in over 90% of cases without needing any software downloads or reformatting! Let me know what you find or if Terminal gives a specific error code.
