At present Hubspot does not appear to have rules for Custom Objects. This is a feature that was introduced in February 2023 for Deals. This feature 'locks' the editing access on Closed Deals to View Only and only allows Super Admins to change these fields. This is an essential feature for Deal but this feature doesn't exist for Custom Objects. Once a Custom Object is moved to Closed we need to be able to limit editing access to Super Admins, the same as Deals.
My company is an works in the insurance space and we have a Custom Object for insurance policies. Once a policy is moved to closed we need to be able to restrict the editing access to all those properties. Otherwise anyone can accidentally change the properties which can create significant issues for us.