Opening a shared project link without signing in now gives you a way to browse the whole project, not just the files the owner happened to leave open.
The project menu has a new Files entry under View. It opens the file tree in a panel on the left - click any file to open it, exactly like the project's members do. Close the panel with the x in its corner and reopen it from the menu any time.
On read-only links the tree is view-only: you can open files, split the editor, and copy paths, but options that would change the project - creating, renaming, moving, or deleting files - are not shown. Links that allow editing keep the full set.