External flash drive permissions 'Custom access' on MacBook

"Custom Access" may mean ACLs are being used to apply different more customized restrictions on those items. AFAIK, the only way to access those ACLs is by using the command line. Unless you are familiar with the command line then I don't recommend using it because there are no safety nets. I don't know whether there may be some GUI app to examine & modify ACL permissions on a Mac.

It does not help that you have neglected to provide details such as the version of macOS being used or the file system used on the external drive(s).

And are you able to still write/save things to that drive?

Is "Ignore Ownership" enabled or disabled on that volume assuming it is using APFS or MacOS Extended file systems?

"I have been using this drive a awhile now, I also have the same problem with folders whereas I used to be able to lock them to 'Write only' but now unable to do so."

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Thanks for the reply!

It might be a reading error from within the user. So, I would try the following...

See if anything here helps.

Try the Following, in the Oder Required...

A. Uninstall Security Software:

Do you have any Security Software installed? If so, Uninstall it, likely with an Uninstaller being required). IMPORTANT: Security Software usually requires an uninstaller to use; just-dragging & dropping it into the Trash and then emptying it the trash will case issues.

B. Reset the SMC and your NVRAM:

(Applies to Intel-Based Macs Only): Sometimes when changes are made to the system(i.e. updates), system configurations (i.e. for Screen) become manipulated, technically. So, reset the SMC and NVRAM

C. Single-Out this User:

What happens when you create a new Administrator user? Do you still get this error? If not, then it it like an issue with the configurations of the current user. If so, then it is an issue of the macOS, in which case, you'd need to reinstall it.

D. Remove ALL Profiles:

Sometimes, profiles are created that restrict usage. Here's one I created back in 2022 --(had to modify a few links. As time went on, old ones provided were discontinued by Apple). Here it is: How to Use a Profile to Disable the iSight Camera in macOS 14 Sonoma - Apple Community

How to find and delete provides...

1. Open: System Settings
2. Select: General
3. Click: Device Management
4. Select: a profile
5. Click: the - button

E. Rebuild the Spotlight Index:

Issues with search results seem an unlikely reason, but it plays a role in locating files. So, try rebuilding it. Go here: Rebuild the Spotlight index on your Mac - Apple Support

F. Reinstall the macOS:

Nothing would be deleted. It's just that items that have become corrupted or deleted, would be replaced or reinstalled back to where they should be. Go Here: How to reinstall macOS from macOS Recovery - Apple Support. Important: Be certain to create a backup of your Mac prior to performing the reinstall. That way, you can have something to restore from the Mac from, should anything go wrong with the reinstall. Once reinstalled, try this once more, seeing if you still get this error.

As a last resort...

G. Reset to Factory Settings:

As a last resort, back up your Mac 100% using Time Machine Backup, and then erase your Mac and reset it to factory settings. Use Migration Assistant to reinstall items. Contact the developers, requesting a new key, if you cannot reinstall it.

“External flash drive permissions'Custom access' on MacBook: I have a external flash drive connected to my MacBook but in 'Get Info' and under 'Sharing and Permissions' it doesn't allow me to lock it with 'write only' just saying 'You have Custom access' This never used to happen. Is there any reason for this please?”

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Troubleshooting 'Custom access' on macOS:

Is this a Never-Used Flash Drive?:

If not, do not perform the flowing , as all files would be lost, If so, perform the following.

Format this to FAT32, if Never Used:

This may be for Windows-Only. Using a Windows PC, format this to FAT32. That should make this interoperable between PC and Macs. Then, if desired, make this of NTFS format on your Mac.

Boot in Safe Mode:

In Sage Mode, Login Items do not open at login, and certain cache issue are fixed. So, see what happens when you try this in Safe Mode: Start Up your Mac in Safe Mode - Apple Support

“Been using this flash drive for awhile now, it is formatted to fat32, I get the same issue with other external drives where it won't 'write only'. I'm using MacBook Pro Tahoe 26.2”

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Provide more in context to my second reply.

Where to go from here:

So, did you perform anything I mentioned? If so, any success? If no success, then it’s probably read/write error, and you’ll have to go with data recovery. On all of my drives that give had, I’ve always purchased that, and renewed it. Why? Because I’ve been through data loss from dropping it in water, which resulted in corrosion.

Two Things:

A. Restore it from a Backup:

Did you create a Time Machine backup of your Mac prior to installing this update? If so, restore your Mac from it. If not, then take this as a learning experience knowing to always backup your Mac prior to installing updates.

B. Report to Apple:

Do Your Part: Provide Apple feedback on this. They won't get back to you directly, but the more they hear of an issue, then the more they'll know what to look for and what needs to be fixed.

1. Go Here: Feedback - macOS - Apple
2. Select: "Bug Report" for the "Feedback Type"
3. Select: "Software/Frimware Update" for the "Feedback Area"
4. Comment: That you came across this issue after installing an update
5. Proceed from there as necessary