From the help for the Get-App cmdlets' "Description" section:
You need to be assigned permissions before you can run this cmdlet. Although this topic lists all parameters for the cmdlet, you may not have access to some parameters if they're not included in the permissions assigned to you. To find the permissions required to run any cmdlet or parameter in your organization, see Find the permissions required to run any Exchange cmdlet.
https://learn.microsoft.com/en-us/powershell/exchange/find-exchange-cmdlet-permissions
If you need more help you should probably use an appropriate Exchange tag to engage with the right SMEs when you post your question. PowerShell isn't the problem, here.