Do you control what you believe?

[Edwardo Piet]

[...]To be honest, I don't know how to function without assuming to believe in free-will.

Then you are confusing determinism with fatalism.

If takes an assumption of a soul for free-will to be possible

I can't conceive of how that would make the libertarian sense of free will possible.

One reason is you don't want to act as if you have no control, while it's possible you do.

We do have control in the sense that we have conscious motivations that come from other conscious motivations that we have. It's just that ultimately that is determined by unconsciousness. We have control, but that's not the same as free control.

But there is no harm in the case of not having free-will, in acting as if you have free-will.

I think there is, for reasons stated above, but it was an off-topic digression. Whether it does any harm is a moral question and not addressing the OP.