There’s a sync_disabled property that is supported and used to prevent certain items from syncing, but it’s not exposed in the UI.
Depending on your use case, you can do it yourself though by running SQL on the database.sqlite profile. The query would be something like this:
update sync_items set sync_disabled = 1 where item_id = 'NOTEBOOK_ID' or item_id IN (SELECT id FROM notes WHERE parent_id='NOTEBOOK_ID')
(replacing NOTEBOOK_ID with your notebook ID)