Scope of FROM email addresses impacted by DMARC (DKIM and SPF)?

We’re working with the HR and Finance departments within our organization to coordinate secure email sending from our Oracle Fusion instance. Each department has its own set of (non-DKIM) vanity email addresses which have previously been used for things like Supplier notifications, Benefits correspondence, etc. We want to fully understand the scope of emails impacted determine what default address would be best for us to use and to better understand what manual configuration changes we may require after defaulting.

We first opened a Support Request as specifically mentioned in the documentation DKIM Support for Fusion Cloud on OCI (Doc ID 2702234.1)