Make Tech Easier published a tutorial about how to mount and access an Ext4 partition in macOS.

How to Mount and Access Ext4 Partition in Mac

If you work with Linux, you probably have a hard drive or two formatted with Ext4 or a related filesystem. Assuming you only work with Linux, that isn’t a problem. When you need to access data from that Ext4 filesystem on another operating system, you start to run into trouble. Macs, for example, don’t support Ext4 filesystems. If you plug a drive in, it’s simply not recognized. Fortunately, there are a few ways around this. 

How to Mount and Access Ext4 Partition in Mac