We are starting with creation a collection for our small archive. The photo collection should be protected. Access wil be given only to registered users and members of the organisation.
A small portion of items should be published to everyone. Is it possible to define that a list of i.e. 50 items are randomly public and others set or private. What exactly means private for collections and items? I can define access to private colletions for user roles. Is it also possible for items?
If at least one item of the collection will be public, then the Collection itself must be public. Being public means that users who are not logged in will see the collection public items list when visiting its link (instead of a 404). But then of course you can have multiple items published as private or public inside that collection. The user roles who can see private collections (all of the private collections) will then be able to browse those collections not only in the admin side, but also in the website, once they are logged in. And yes, there is an extra level which is to say that this user role can also see the private items of that collection. Usually it is expected the first grant to derive the second, but you may have a special case for that.
The only thing I’m no 100% sure is your request for randomness… the item privacy is the one it has, period. You can, from a selection of public items, select a few to display in a page using our Gutenberg block, if that is what you have in mind. There is even a Pull Request open for using “random” sorting in those Gutenberg blocks, which I hope will be merged in a few versions: