The question appears in variant forms1 just to say it is ridiculous on Android that ext4 is the default file system that doesn't recognize USB pen drive formatted with ext4 (but Android 4.4 recognizes it without any problem). As a Linux user, this is a big regression, and I still have not found a way for a USB to be detected as a USB, like pens with FAT32 or NTFS. I have root on my device.
1 Related questions:
We still need root. First I need to make a dir in /data/media/0/ (/sdcard)
mkdir /data/media/0/usb1/
which means USB is not detected as USB ever, but I can read data from apps that it is what I want.
After I made a script with:
su -mm -c "mount -t ext4 /dev/block/sda1 /data/media/0/usb1/";
su -mm -c "mount -t ext4 /dev/block/sda1 /storage/emulated/0/usb1/"
and using Script Manager - SManager, I made a favorite script and with the add-on to create a launcher, I made an icon on the home screen (I preferred shortcut instead of the widget), and on clicking it, it mount my ext4 USB pens.
That said, I find it easier to use a custom kernel that allows this without needing an app. That's how I overcome the limitation and could be one option
– beeshyams Nov 21 '18 at 04:26