If you want to make a solid back up of your whole drive without restoring it to a new machine, this is your best option.

There are a couple ways to accomplish this, but either one will require another Mac and a destination drive to clone the one from the dysfunctional machine onto.

Apple built this capability into the Disk Utility App right in macOS. In most current versions of the operating system, it works best if done from Internet Recovery to avoid any background access to the disks.

You can use this method without installing the OS on the target drive as well, but the result will not be bootable.

Third party software also exists if Disk Utility does not work, or gives an error, but this software may not be free.