Hi @Anonymous
Please check my earlier post. Here I declared a variable called Filename then value as Test.csv. Then I used the split().

In your case you have
first(split(variables('triggerOutputs()['headers']['x-ms-file-name-encoded']'),'.'))
Not sure this is correct.
You can move the triggerOutputs()['headers']['x-ms-file-name-encoded'] under the initialise value part.
Then map the variable under the expression.
Thanks