Create a shared channel if you want to work with people inside and outside your team or organization.

Only team owners can create shared channels. As the team owner who creates the shared channel, you become the channel owner, and the channel inherits labels from the host team.
Shared Channels, one of Microsoft’s most anticipated updates, is now available to all tenants. It allows users to have seamless collaboration both within and beyond organizational boundaries. The highlight of shared channels that grabs a lot of attention is users don’t need to switch tenants to collaborate outside