anonymous user, Thanks for reaching out. unfortunately, this is not supported, as per the documentation,we cannot move Microsoft.web/site/functions
from one resource group to another or in between the subscriptions as well.
Alternatively, as a workaround you need to modify your project/source code and redeploy to a different function app with only one function created (as per your requirement).
I would suggest you raise a feedback request using the link.
Feel Free to reach back to us if you have any further questions.