[question] How can I set an implicit user change in a workflow?

[Vic-Skr]

Good afternoon.
Case 1: in a workflow, I need to assign responsibility for a record not to a specific user, or a group of specific users, but to the author, that is, take the value of the “created by” field. Is this possible?
Case 2: in the “Project Tasks” module (for example), in addition to the “Responsible” and “Share with users” fields, I need to add another field of the “User” type - in order to select users related to the record. And then be able to change the Responsible field in the workflow to the value of this new additional field. How can i do this? Currently, there is no way to create a field of the "User" type in the field editor.
Thank you in advance for your answers!