The closest feature request / bug report that fits this is Synchronize should also upload locally created files 路 Issue #8078 路 nextcloud/android 路 GitHub
If you think this is important, then I suggest you vote on this.
Is there an issue on github that is specific to implementing the same feature as it exists on desktop? That means:
- select a local folder to sync
- select the remote folder that it should be synced with
- automatically sync all modifications of existing files and folder + new files and folders
Edit
There are many issues on this, but probably these 3 are the ones should be voting on: