So according to google it's possible to add additional accounts to a game as contributors or collaborators. However I'm not seeing this option anywhere in the "edit project" interface. So how do I do this? My aim here is to give someone credits but not full admin rights.

I think there's some confusion.

Itch only allows you to add a "collaborator" as an "administrator," meaning they can edit the page and the game.

As far as I know and have read, Itch doesn't have a system for listing the "collaborators" who have helped you; in other words, it doesn't have a system for crediting other users.

What I've seen is that it's always done manually. You create a table on your page where you list the people who helped you with the project, with a link to their profiles.

Contributors can create a collection of games they've worked on and then add that collection to their profile. But all of this has to be done manually.