Is it this line which let’s me know this is an ISR function:
< x-nf-render-mode: odb ttl=60
The way that the functions handler is created is by parsing the HTML in the post-processing on the build. As this page is handled by a function, there is no HTML file to process. The solution for this is to manually create an HTML file which contains that form and then include that HTML file in the deployed site.
As long as the form the function makes exactly matches the HTML form, the form in the function will work.
Also, if you make changes to the form the function creates, please remember to also update the HTML-only version of that form at the same time.
If there are other questions about this, please let us know.