Hello @Pramod_Bangalore,
For Octo-SPI mode, ten GPIOs are needed, when one memory is connected. An additional GPIO for DQS is optional for the Regular-command protocol and mandatory for the HyperBus protocol.
According the memory datasheet the DQS is available and you can used.

For pin assignment you can use STM32CubeMX or you can refer to STM32U575 datasheet table 26.
I recommend you to look at How to reach the maximum OCTOSPI frequency - STMicroelectronics Community for OCTOSPI hardware recommendation.
Also, you can find in Getting started with STM32U5 MCU hardware development application note how to use the STM32U5 series microcontrollers and describes the minimum hardware resources required to develop an application using these MCUs.
I hope this help you.
Thank you.
Kaouthar