Where is the saved page file

Where is the saved page file generated by Groov_serv_win? Why can’t I find it?

Are you referring to the new-ish groov Build option: File > Export?
If so, the json file that’s created should go to wherever your downloads go in that browser, usually your Downloads folder.

Not a exported file.
Is the page file that groov serv-win produces for browsing

The pages that groov displays while browsing it are generated dynamically via JavaScript: they don’t exist on disk in any rendered form.