Hello gemmajoom,
Thank you for bringing this to our attention, and sorry for the inconvenience you're experiencing.
The latest version of SP Page Builder allows adding multiple file extensions to the File Field. Please ensure your installation is up to date and try this functionality again. If the issue still persists, please let me know and I will investigate further.
Regarding the Option Field, it currently supports only single selection. Multiple selections are not yet available, but we've noted your feedback and will share it with our development team for future consideration.
To display only an icon for the Link Field, you can add an icon element and insert a space in the "Link Text" field. This will hide the URL text and display only the icon that links to your file. Hope this helps!
Thank you for your understanding and patience.
Best regards