A few reports on the Pi forums of similar issues with no good solution, so sharing this fix:
TLDR – resolution in last paragraph.
After first of all being unable to start the write to SD cards with Raspberry Pi Imager (RPI) (even though it prompts for your password when you attempt to write, and therefore you think you are granting the program permission to do what it needs) I[b] granted RPI “Full Disk Access” [/b]permission from within MacOS System Preferences (system preferences > security settings > Privacy).
After restarting Raspberry Pi Imager (RPI) the write process would start, however it then fails to complete the imaging process after verifying disk and moving to “waiting for Fat32 partition to mount” (or similar wording). This then leaves the SD card unmountable until it is erased with a new boot partition from within Disk Utility. I tried multiple brand new, brand name SD cards.
Granting Full Disk Access” under system preferences > security settings > Privacy worked for BalenaEtcher which wrote SD cards fine. So the behaviour of RPI was confusing. However, I really wanted to use the advanced settings in the Raspberry Pi Imager program to setup the Pi with changed username, SSH and public key etc.
Solving the issue:
I removed “Full disk access” permissions and instead used the “Files and Folders” option to grant RPI “Removable Volumes” permission.
Restarted RPI and attempted another write and It completed successfully.
System specifications
MacOS Monterey 12.3.1 on Apple M1 MacBook Pro
Raspberry Pi Imager v1.72
Anker USB-C SD / micro SD card reader
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