Whilst New-CsGroupPolicy Assignment is in 1.1.6https://www.powershellgallery.com/packages/MicrosoftTeams/1.1.6
It is currently limited to the following policy types: CallingLineIdentity (Caller ID policies), OnlineVoiceRoutingPolicy (Voice Routing policies), TeamsAppSetupPolicy (App Setup policies), TeamsCallingPolicy (Calling policies), TeamsCallParkPolicy (Call park policies), TeamsChannelsPolicy, TeamsComplianceRecordingPolicy, TenantDialPlan, TeamsEducationAssignmentsAppPolicy, TeamsMeetingBroadcastPolicy (Live Events policies), TeamsMeetingPolicy (Meeting policies), TeamsMessagingPolicy (Messaging policies), TeamsUpdateManagementPolicy.
So TeamsAppPermissionPolicy not currently supported per documentation
I have opened a uservoice for you herehttps://microsoftteams.uservoice.com/forums/555103-public/suggestions/41511472-new-csgrouppolicyassi...
Would recommend you vote on it to push it up the agenda