ext4 is only supported for the internal storage.
SODP uses mainly AOSP and AOSP doesn't support ext4 by default.
So teach VOLD in SODP AOSP the usage of ext4 in sdcards via a commit.
PR's for A10 Custom ROMs
http://gerrit.aospextended.com/c/AospExtended/platform_system_vold/+/412/2
https://review.lineageos.org/c/LineageOS/android_system_vold/+/258169