I'm working with a Mavic 3 (normal, not classic, not cine, not enterprise).
The zoom works pretty much as I would expect when in video mode.

When it is in photo mode, the zoom seems to be 'fixed' on either 1 or 7 with no option via the wheel or screen to change it.  Is that normal?

Yes it is. You can use the explorer mode to do this.

Hi there. Thank you for reaching out. The normal photo mode for the DJI Mavic 3 only supports switching from a Hasselblad camera to a telephoto camera, only 1x and 7x can be supported. You may choose "Explore Mode" to perform the said feature. Should you have other inquiries, please don't hesitate to reach us. Thank you for your valued support.

Since the so-called zoom with a fixed focal length is not really a zoom, but only the "definition of a section in relation to the center of the picture", it is better to do it on the basis of the RAW photo format in post-production...