I want to make sure I understand that are you using the app as an end-user looking for a built-in print button, or are you the app developer building this screen?
If you are just using the portal right now, click into the PO record, press Ctrl + P in your browser, and set the destination to "Save as PDF" or your physical printer (adjusting the scale to "Fit to page" so nothing cuts off).
If you are designing the app, standard practice is to add an icon or button with the Print() formula on its OnSelect property, which triggers the native browser print dialogue for that screen. For generating clean, formal multi-page PO documents rather than raw screen captures, pair the button with a Power Automate flow that populates a Word template and exports a clean PDF.