A guest will need an account to work in the project yes. The blog post is correct: share button at the top, then add the email. What is not working exactly?
I did try to do what the blog post says, went to share button, typed in email address but I don’t seem to have any option to “Select Only this Project (Guest)” like the blog post says? Here is a screen cap of what I see.
That doesn’t actually address the problem in this thread. The blog post still says “Then select ‘Only this Project (Guest),’” and the linked article doesn’t mention that this step is no longer needed.