How to access an EXT4 format external disk in Windows?
There are certain drivers and applications you can download for free and run on your Windows PC to access (read & write) data on an EXT4 partition or drive.
Ext2Fsd is an open-source driver for computers running Windows. You can download if from the official website for free here.
Another option is Freeware Linux Reader for Windows which provides read-only access to file systems such as EXT4 and Apple’s HFS and HFS+ file systems. This is a free standalone app.
You can also try Ext2Read which again provides read-only access to EXT4 disks and partitions.