I have developed a local splash screen to direct users to a story map in multiple languages. The file is stored locally and the whole setup runs in a kiosk environment. I would like users to be able to return to the splash screen but since the browser runs in a kiosk environment there is no browser navigation, so this needs to be done via a button within the story map. I tried to set it up but storymaps automatically converts the link <C:/User/documents/filename.html> to <https://C/User/documents/filename.html>. I tried to use <file:///C:/User/documents/filename.html> (this is the pointer used in the kiosk options in the system settings but this doesn't work either. This link is either automatically removed or converted into a https address.
Is there an alternative way to insert a hyperlink to a local html file or is this a bug and if not, what is the rationale behind disallowing the use of local html files within a story map?
It's an intentional feature of AGOL / Portal to automatically adjust URLs like that, and you won't be able to use a file URL or local filepath.
You might configuring the kiosk machine to run IIS and add the file location to a virtual directory, then your files would be accessible via URL.