Access encrypted Ubuntu disk on macOS
Unfortunately, there is no native method to access an encrypted Linux volume on macOS.

A technique that may work for you is downloading VirtualBox (a free and open source virtual machine program), installing a Linux distribution in a VM, setting the host (macOS)'s /dev directory as shared to the VM, and then try to mount the disk on the virtual machine, through the shared /dev file. The likelihood of this working is not great, but it might work. Can't hurt to try.