There are plenty of police reforms that could be enacted from a libertarian perspective that would improve matters. Qualified immunity reform is libertarian. Holding police accountable for misbehavior is libertarian. Reducing the power of police unions is libertarian. Getting rid of overtime and pension abuse is libertarian. Banning no-knock raids is libertarian. Reducing bloated police department bureaucracies is libertarian.
Broader reforms that would reduce the need for police and reduce police/civilian encounters are also libertarian. Getting rid of victimless crimes, especially the drug war, and certain categories of criminal business regulation that should be handled civilly is libertarian. Getting rid of taxes that lead to black markets that in turn lead to police/civilian encounters is libertarian. Abolishing laws that allow local governments to put people in jail for failure to pay civil fines is libertarian. Separating forensic science services from prosecutors’ offices is libertarian. Holding prosecutors accountable for misconduct is libertarian. Finding alternatives to prison for certain categories of offenders is libertarian.
By contrast, “defunding the police,” if that just means willy-nilly cuts, is not libertarian.
If you get rid of the police, they will be replaced by vigilante justice and mob “protection.”