"Can you invite people from outside an organization into one of its spheres?"
To be able to invite an external person to join a sphere as a visitor, you must first activate the "Visitors can connect" function in the sphere settings to authorize visitors.
After activating this option, you must refresh the page in order for the modification to be taken into account.
When you invite a new person to join the sphere, they will be considered a visitor by default unless you check the option to add them as a member of the organization.
Note: A visitor cannot access the members portal or see the other spheres in the organization.
Within the sphere, a visitor has the same rights of reading and writing, and access to collaboration tools, as sphere members.