I like this idea. Would be cool if the guests could mark items as purchased and would only reflect to other guests and not the admin 😂 at least not until after the event.
I know it isn’t specifically what you are looking for since it isn’t self hosted, but Things to get me is great and I’ll take any opportunity to get people off of Amazon that I can.
You could probably make a new issue in a wishlust repo that uses markdown checkboxes or something similar. Would be good if you already host Gitea or another git sever.