On my new M1 MacBook Pro running macOS Monterey, I found that I couldn’t create folders or change the “read-only” permissions on an external hard drive that had previously worked fine on my old Mac. Even after unlocking the permissions and trying to change access for “staff” and “everyone,” I got a message saying I didn’t have the necessary permissions. I tried entering Recovery Mode and disabling System Integrity Protection (SIP) via Terminal, but the issue still wasn’t resolved.
Have you checked the file format of your external drive? If your external hard drive is formatted as NTFS (commonly used by Windows), macOS can only read it by default, not write to it.
Therefore, you need a tool to write NTFS on Mac, such as iBoysoft NTFS for Mac. Simply download, open, and mount your external hard drive, and you’ll be able to read and write to NTFS-formatted drives on your Mac right away.
The most straightforward method is to use Disk Utility to erase the drive. Formatting will erase all data, so it’s recommended to back up your data first. Then, use Disk Utility to erase the drive and format it as exFAT or APFS (for Mac use).