Welcome to Microsoft Q&A! Thanks for posting the question.
If you are creating the storage trigger from azure portal and while creating the storage trigger you are specifying the path as starting with '$' then as of now the portal does not allow and I have reached out to my team to confirm if this is issue with the validation or expected behaviour.
As the workaround you can set the path in the function.json and it works as expected. I have tested the same using azure portal, python VS code, C# visual studio.
Feel free to get back to me if you need any assistance.