How to give user access to only one folder

I am quite sure it was asked before but I was neither able to find or not able to word it for success.

Just to make sure I have not misunderstood something. I use Nextcloud for several purposes of collaboration/groups, one is for image development, for which I created a group folder. I created a group for the Graphic Designers for them to access all sub-folders. Each subfolder is named after one client. I have now added a client as a user. But it seems that I cannot grant access to only his subfolder by just assigning to him. I must use the sharing icon. Is that correct?