Could you clarify why you think this is so? As an owner, my interests would align with the DPO's interests so it's hard to me to find where the conflict of interest would reside in the case of being the sole employee _and_ DPO.

Now if it's a large company where they make money per GDPR policy workaround then I could see it being required another person than the owner, but it could still certainly be an employee.