You have a Microsoft 365 E5 subscription that uses Teams. A group named Group1 collaborates with users from a partner company named fabrikam.com. You need to ensure that only the members of Group1…

An app setup policy manages the availability and pinning of Teams applications for users, and has no direct relevance to creating shared channels or inviting external users.

For members of Group1 to invite users from fabrikam.com to shared channels hosted in your organization, your Azure AD cross-tenant access settings must configure inbound access for fabrikam.com. This allows fabrikam.com users to participate in shared channels hosted by your organization.

To control which users can create shared channels, you must configure a Teams policy (specifically a Teams messaging policy or a Teams policy with shared channel settings) and assign it to the members of Group1, granting them permission to create and invite external users to shared channels.

While configuring outbound access settings for B2B direct connect with fabrikam.com is part of establishing the overall B2B direct connect relationship, the specific requirement for our users to invite fabrikam.com users to our hosted shared channels primarily relies on our tenant allowing inbound access for fabrikam.com users.

"Configure Teams settings" is too broad; the specific policy required to control shared channel creation by a group is a Teams policy.