Is it possible as an admin to share a folder of a file on behalf of someone.
What I can do, is create the an share and then do a files:transfer-ownership, so that the share and folder gets to that user, and disjoin that share?
Nextcloud version 10.0.2
No, if you want to control the files, you have to share them from an admin account to the user (and then you can also provide some files to other users as well). The philosophy of Nextcloud is that you control your own data, so the admin can’t easily share or modify your data (sure, he has finally access to the file system).