This research investigates the feasibility of employing polarization multiplexing in OAM (Orbital Angular Momentum) transmission, which is anticipated to be a prospective technology for the sixth-generation mobile communication systems (6G) expected to realize by 2030. Specifically, focusing on the advantageous property that OAM signals can utilize polarization multiplexing alongside mode multiplexing, we conduct an analytical assessment of the system capacity for MIMO-OAM incorporating mode and polarization multiplexing. The numerical results indicate that the effectiveness of polarization remains consistent regardless of the number of MIMO streams in scenarios without mode limitations. However, it was observed that in cases where mode limitations exist, the effectiveness of polarization diminishes due to the decrease in stream power attributed to polarization at relatively longer link distances. Furthermore, increasing the number of MIMO streams was found to enhance spatial diversity effects, thereby boosting system capacity irrespective of mode limitations.