A Mac is not supposed to read ext4, that is Linux. You can ignore the problem since it is your Linux VM which is the one reading the SD card. FYI, make sure your VM is Ubuntu 18.04, not 16.04.
Once Linux is running, just give ownership to the Linux guest system, and it will know how to work with ext4. However, don’t expect everything to just work, most of the time VMs need work, for example, and forcing ownership of the recovery mode Jetson to go to the guest o/s and to not be interfered with by the host. VMs are not officially supported.