Hi Saurabh,
Could you see the external OSD through console command?
Moreover, List of SPI writes that we shared earlier was used by you?
Regarding external OSD input source setting, you can refer the function EXTOSD_FUNC_setInputFormat which is available in external OSD firmware file (vsp_osdeg_extosd.c).
Best Regards,
Jeyasudha.M