The ASUS PRIME B450M-A II motherboard is compatible with the ASUS Dual RX 6600 graphics card in terms of physical connectivity, as it has a PCIe 3.0 x16 slot that can accommodate this graphics card. However, it's important to note that the RX 6600 can run PCIe 4.0, but will be limited to PCIe 3.0 on this motherboard, which could have an impact on performance.

In addition, make sure that your power supply unit (PSU) is powerful enough to support the power consumption of the RX 6600, which requires at least 450 watts.

To sum up, physical compatibility is assured, but it's crucial to check the power of the power supply and consider the potential limitations associated with PCIe 3.0.