Sharing & Permissions on SSDs: "You have custom access"

You may need to first erase the drive using Disk Utility before the drive can be used with macOS. I've seen reports that if Windows 10 formats a drive with ExFAT that it may use a larger block size for the file system which macOS doesn't recognize.

Make sure to backup any data from the drive before erasing the drive.

maybe....simon0672. plug them into your MacBook Pro 16" , both should work, for now. click on them after they appear on your Desktop, and do a get info on them (*command/Apple+I) and down at the bottom of the info window that comes up for each drive you should see sharing and permissions, and a padlock. Believe it or not, the default for Catalina is to make all drives read-only, not read and write. You can change this. click the padlock at the bottom of the window to unlock it. You'll need your user/login name and password which you'll be asked for, and then click on the user on one column, and see what that's set to. If it's read, set it to read and write, same goes for system. Apparently Catalina does stuff a little differently and introduces System Integrity Protection (SIP)

I hope you're not as confused as I am

jb

simon0672 Said:

"[...]When I 'get info', both drives have 'You have custom access' under Sharing and Permissions, and there seems to be no way to change that. I suspect that is the reason?[...]"

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Firewall Settings:

Do you have Security Software installed? If so, uninstall it (get the uninstaller from the manufacture and nowhere else. Elsewise, it could end up being Malware or Spyware you install). It has firewall settings which disallow connected devices. Security Software gets in the way on a Mac, and this is a put example of how.