What I think could be helpful is an account-wide search functionality.
It could be a search box in the navigation menu on the left, which is visible and accessible on any page within the Experimentation UI.
The user can enter anything, including names, keys or IDs of experiments, pages, audiences, attributes, events, etc.
The search algorithm then looks up any matching elements from all projects that this user has access to.
Besides the main input field for the search string, there could be filters for specific element types (experiments, audiences, events, etc.
The search results should show the project that the elements belong to. There should be a filter option to only show matches from the current project.
The search results should be shown in a dropdown list (a modal, for example on the current page, not mmediately navigate away to some "search results" page.
When the desired element is found, a simple click on the element should lead the user straight to the element in question. This should probably open in a new tab, not to accidentally have the user lose their work on the current page.
For example, the user is creating an experiment and wants to check which Audience or Page to use. So they search for an applicable element and want to look into its details. That should open in a new tab, not to abandon the experiment they're just setting up.