Thanks for reaching out to Q&A.
As the message in the portal states, the function may have been edited or created through an external editor ( say Visual Studio, VS code , etc). In this case, portal editing will be disabled, it is by design. You will have to choose a development environment such as Visual Studio, VS code to create a function and then publish to the Azure runtime. Post publishing, the functions will appear in the portal.
I hope this helps! Feel free to reach out to me if you have any further queries.
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