Is there a way to dictate text into a document on a Mac Studio without buying a third party app?

Yes. See the following support document for details. click here ➡️ Dictate messages and documents on Mac - Apple Support

It should appear anywhere text can be entered if the Microphone option is available for it.

PowerPoint may handle dictation differently than Apple's native apps.

See Microsoft's help website for details: https://support.microsoft.com/en-us/office/dictate-your-presentations-and-slide-notes-in-powerpoint-97f3373e-58b9-4e39-b413-83d6d2c09055

You should get a pop-up dictation icon when it is running. It works fine in Powerpoint.