Please check if the F&O derivatives segment is activated for you. To do this, please follow the steps below

Double click on your name and check exchanges - (NFO should be enabled) -
If yes and still not able to add scrip of F&O then clear the app data and check
To learn how to clear your app data, you can follow along with a similar problem-based article here

When both cash and collateral margins are available, which one is utilized first? What is the order of utilization?
What is the margin blocking percentage during the end-of-expiry week for physical settlement of stock option contracts?
Can I do intraday trading in stock options?
When does expiry take place for Nifty, Bank Nifty, Sensex, Bankex, and stock option contracts?