Configuring client to sync to server rather than from server to client

Tried nextcloud-client levels
nextcloud-client-2.5.3, and

The situation is a pain full migration from owncloud to nextcloud. We won’t go into the details, but needless to say pain full.
I am using nextcloud as a backup for my client laptop. The files to be synced from the client are all in one folder. That worked to ownCloud for several years, from version 4 to version 9.
In the process of migrating to nextcloud I had ended up re initializing the sync folder on the server. The data on the client is still valid and I have a copy of the server just in case.
I would like to configure the client to sync the client folder to the server. The configuration process only seems to recognize configuring syncing from server to client.
How to I configure sync from client to server when there is initially no corresponding folder on the server?
Thanks - Dan

There does not appear to be a way to actively manage the source list. However if the sync is run on the source client folder the sync list is generated. It is not updated in real time; but only after the sync is complete.