Explanation
Making a field universally required is a way to ensure that the field needs to be filled on every record; it prevents users from saving a record without entering a value in that field. It can be used to ensure that the billing system field needs to be filled on every invoice record by making it universally required in the field settings. Creating a process builder to set the field, defining an approval process for the child, or requiring the field on the record type are not ways to ensure that the field needs to be filled on every record; they either do not enforce data entry or only apply to certain scenarios or users. References:
https://help.salesforce.com/s/articleView?id=sf.customize_fields.htm&type=5