To update Compliance Categorization for Salesforce uneditable Standard Fields, we have to set complianceGroup through deployment.

1. Extract the Account Object BillingAddress field.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
    <types>
        <members>Account.BillingAddress</members>
        <name>CustomField</name>
    </types>
    <version>59.0</version>
</Package>

2.Add complianceGroup value to the extracted field and deploy the field.

<?xml version="1.0" encoding="UTF-8"?>
<CustomField xmlns="http://soap.sforce.com/2006/04/metadata">
    <fullName>BillingAddress</fullName>
    <trackFeedHistory>false</trackFeedHistory>
    <trackHistory>false</trackHistory>
    <complianceGroup>PII</complianceGroup>
</CustomField>