Is touching doorknobs without sanitizing them after touching personal belongings contaminated with the virus, with the thought that it is negligence and carelessness, considered involuntary manslaughter that requires repentance, or could it amount to voluntary manslaughter, bearing in mind the presence of obsessive-compulsive disorder?

You did well in taking preventive measures. There is no need to worry about people contracting infection from touching handles without sterilization; infection is not inevitable. "No infection" means that the disease does not transmit on its own, and a person may become ill without infection. If someone does get infected after touching the handles, we cannot definitively say that it was because of you. Allah is the Doer of all things, and therefore, nothing is incumbent upon you.