The Elektron C6 utility is a 32-bit application and is not supported under macOS 10.15 (Catalina) or later. C6 will not be updated further, instead, we recommend using Elektron Transfer for transferring samples, sounds, presets, and OS updates to your Elektron device.

Elektron Transfer does not support SID Station, Octatrack MKI/MKII, and Analog Drive. For Monomachine and Machinedrum (all versions), only OS transfers are supported.

You can download the Transfer utility here:

Another possible (non-Elektron) replacement for C6 is SysEx Librarian.