Hi Dan,
As I've explained above the image classification tools are greyed out and unselectable. I have read the documentation you have posted, but the greying out of the tools prevents both approaches being tried. I am assuming that this has something to do with the status of the spatial analyst extension/installation as I do have the extension assigned by our administrator from AGOL. I can see no documentation now on how to ensure that the extension is present and enabled in Pro. As you noted, it used to be a case of manually enabling it in ArcMap, but this is no longer the case in Pro.
Edit - I have looked in Licensing within Pro and confirmed that Spatial Analyst is enabled, yet still upon selecting a raster (jpeg or img) the classification tools and wizard remain greyed out.
I would like to solve this early this week if possible, so any further responses are welcome.
Thanks,
Chris