I’m currently not a user of the nextcloud app client, so others might chime in and better help.
Recently though I looked into bi-directional sync support in /e/s implementation and also into nextcloud - a long thread on it seemed unresolved: https://github.com/nextcloud/android/issues/19
A developer posted a solution on bi-directional webdav sync (“Easysync”), maybe it helps you out? https://f-droid.org/packages/com.phpbg.easysync/