Q: Is via P2P direct access with the mobile app possible - without a router?
A: No. For the P2P access always an Internet access is needed. But if you only want to access the camera locally - without Internet access - you can directly connect the camera via LAN cable s.Calculator.
For access via mobile phone, a wireless router is required. However, this router does not require Internet access.
A remote access is not possible then of course.