1-a adb push busybox-*** / ; adb shell
1-b chmod a+x busybox-* ; busybox mkfs.vfat /dev/block/bootdevice/by-name/userdata
2-a unmount data
2-b adb shell ; mke2fs -t ext4 /dev/block/bootdevice/by-name/userdata
At this point it is Ext4, but it may be vfat in TWRP advanced wipe page.