Workflow optimization and employee morale will still be important under socialism.
Workflow optimization is just management of people/resources/timelines (and is present in non-repetitive jobs too): what processes aren't working well together, what were the root causes of issues we encountered, how do we fix these problems? This, too, gets better with experience and study and some workers should specialize in this sort of management.
Employee morale (and other aspects of emotional work) will also still be a relevant question under socialism: how do you balance a specific worker's development interests with the needs of the job, how do you manage interpersonal conflict, how do you build consensus for or mediate disagreement raising from decisions the group needs to make? Straight-up boring old motivation questions also do not disappear just because workers have a stake in the fruits of their labour.
I think you are very narrowly defining manager as a manager of capital (i.e., seeking to maximize profits without care for what products are being made). I think you should read this: https://redsails.org/the-relationships-between-capitalists/
It is only the last part — the coercive, adversarial role played as representatives of capital — that will become obsolete. The coordination part of management (which includes coaching and motivation and conflict resolution) will remain.
My experience with organizations, from families to RPG groups to community associations to capitalist enterprises, is that in a management void, some people will take on management responsibilities. Since these roles require skill and entail responsibility for certain tasks, it's better to formalize it and train people for it. Do you not also see this in the organizations you are part of? Or could you be underestimating the amount of labour others are putting in to managing your community?