You can use "auto download limit" feature to automatically download files in folders and sub-folders which are already in expanded state in your local machine. Files won't sync if parent folder is still a placeholder folder in odrive.
To recursively sync all files and folders, I believe you should set "Sync folder rules".
Set download to Everything
Set include Subfolders to "Checked"
Save and apply to new files and folders to "Checked"
Find more details here: