Hey @Joseph! The ‘All’ button should not be part of your CMS Collection nor any multi-reference field. An ‘All’ clears all filters and displays the initial un-filtered list.
I’ve created a guide here → How can I add and style an "All" button for CMS Filter on adding and styling such a button. I used a non-cms button with the attribute fs-cmsfilter-element = clear and styled it appropriately.
Take a look at the guide and let me know if you need any extra help 