You currently have the filter set to only display the category that you put into the input, so when you click a new item, you remove the old item selected and add the new item selected from the list. This will only allow 1 item from the dropdown list to be selected, filtered, and displayed at a time.
Here’s how to get it to work:
Add a many-to-many relationship between the user and the collection you’re trying to filter. Have 2 lists. 1 list will be “Collection > All records” and then the 2nd list will be “Collection > User relationship records”. Set visibility on the first list only visible when all records where user relationship contains user count is equal to 0. Set visibility on the 2nd list to only visible if all records > relationship > contains logged-in user count is not equal to 0.