By default users added to a Microsoft Teams Team that are external users i.e. guest users have a reduced feature capability set compared to an internal user.
For instance, in peer to peer conversations a guest user can perform a private group chat, but audio and video functionality is not allowed due to license restriction
In a Team the guest user has the ability to chat and collaborate with internal users within the Team and join a Teams Team Meeting with audio and video capability. However, they are not allowed to create a meet now by default.
If you want your guest users to be able to create Teams Team Meetings (Meet Now) then you can do this at tenant level by executing the following PowerShell
Set-CsTeamsGuestMeetingConfiguration -AllowMeetNow $true
Now Guest users will be able to create meet now meetings within a Team
If you want guest users to be able to use audio and video in private chats and private group chats then execute the following PowerShell
Set-CsTeamsGuestCallingConfiguration -AllowPrivateCalling $true
After this setting has applied, Private Calling will be allowed.