I use orgzly [1] and configure it to "sync" to Syncthing's local folder [2] (which Syncthing then syncs). This requires write access to Syncthing's data directory though, so I'm not sure it works on stock Android.
[2] e.g. configure a "directory repository" with content://com.android.externalstorage.documents/tree/<device id>%3AAndroid%2Fdata%2Fcom.nutomic.syncthingandroid%2Ffiles%2FSync%2Forg
[1] http://www.orgzly.com/
[2] e.g. configure a "directory repository" with content://com.android.externalstorage.documents/tree/<device id>%3AAndroid%2Fdata%2Fcom.nutomic.syncthingandroid%2Ffiles%2FSync%2Forg