Can I control sharing Brand Showrooms?

For each Brand Showroom you can set it to private or public. If it's private then only other users on your team will be able to view it. If you're the admin or the user who created the Brand Showroom then you'll be the only user with the ability to edit it. With a private Brand Showroom you can give specific users access to view it by adding their email under "Sharing" within "Settings" for the Brand Showroom. If it's public then anyone with the link to your Brand Showroom can view it.