There's no one-click solution to block all non-Microsoft apps, but with a focused approach, you can closely achieve that goal. Diving into the Microsoft 365 admin center is your first move. Here, you can adjust settings that dictate which apps are allowed. Essentially, by setting up a whitelist of approved Microsoft apps, you're indirectly blocking all others. Creating a SharePoint app catalog can help manage this list, making it easier to oversee which apps are permitted. Further refining app permissions within the admin center lets you specify allowed apps more precisely. For deeper customization, PowerShell scripts offer granular control over app permissions, allowing you to tailor the environment to your security standards. Communication with your users about these changes is crucial to ensure smooth adoption. Also, staying updated with Microsoft's enhancements can provide new tools for managing app permissions. In situations where the built-in controls aren't enough, third-party security solutions may offer the detailed management you're looking for. By focusing on allowing only approved apps, you effectively safeguard your network while keeping the administration manageable. If you need more detailed guidance, Microsoft support and Microsoft 365 specialists are valuable resources.