Unable to activate APFS volume - DiskManagement.disenter-Fehler 0. - externe APFS Festplatte nicht aktivierbar

Try running First Aid on the Container. Even if First Aid reports everything is "Ok" click "Show Details" and look for any unfixed errors or warnings. If there are unfixed errors, then you will need to erase the whole physical drive if you want to continue using it. Make sure to have a backup of the data or temporarily move the data to another drive as erasing the drive will destroy all data on the drive.

This assumes that the drive is healthy. You can check the health of the drive by running DriveDx. In order to access the health information on an external USB drive you will need to install a special USB driver (DriveDx will prompt you when trying to check the health of a USB drive). Post the health report here using the "Additional Text" icon which looks like a piece of paper.

If you have a 13" non-Retina model, then you may also have a bad hard drive SATA Cable. The hard drive SATA Cable on the 13" model has an extremely high rate of failure.

Hello Mar_rsh,

It sounds as though you're attempting to access data from an internal hard drive that was in another Mac. If so, you would have to start up using that disk to access those details as it won't function like an external hard drive on your current Mac. You can find the steps for changing the startup disk in the following article.

Change your Mac startup disk

Have a great day.