On iOS, an error toast appears on the iPhone screen when `File.DeletefileName` is executed, and then disappears

On Android, no problem.
Am I assembling my blocks incorrectly?

That No Available Assets default return value looks fishy.

Try returning an empty text block if not found, and drop it into a variable for testing before jumping into using it for display or delete.

Yes, but the File.Delete method works only with the File component (after File.SaveFile method) on iOS. However, the File.SaveFile method does not return the file path of the saved text file.