Check your permission scheme, look who has the assignable user permission.
I have given the user the administrator role. Still I don’t see him in the assignee list when I want to assign a task to the other user after adding a comment or changing the task status.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.
Admin does not mean "can do everything", it means "can do admin tasks" (admin can do everything is a dreadful approach and Atlassian don't do it). You need to add them to a role that has the assignable user permission, as Udo says.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.