Hi @Anonymous,
No, all Portal actions are done via the default admin context (SYSTEM), and audit isn't setup to show the Contact table.
What you can do is add a "Modified By (Contact)" lookup to the tables in question, enable it for auditing, and then ensure your Portal update scenarios fill this field. As such, each time those fields are changed you'll be able to identify which Portal contact did it by that field changing. You can also leverage this on the Portal forms, and in Dataverse forms/views to identify directly on the table who last performed an action, if that's helpful as well.
Example of this can be found in the gifs of this post of mine - scroll down to End Result and see my forms after create/update: How to Differentiate Draft and Submit on a PowerApps Portal Form | Justin Burch
Examples:
Entity Form: Create Entity Form Metadata for Attribute = Modified By (Contact)

"On Save", Current Portal User, contactid

Web Form: Same, but in Web Form Step use Web Form Step Metadata
Power Automate / Flow: Fill via update package