Which government exams after 12th are conducted every year?

I wrote SSC CHSL twice. Even if you fail once, you can try again next year. Regularity of these exams makes preparation easier.

SSC CHSL, SSC GD Constable, and Railway exams are conducted regularly every year. Defence recruitment like Army GD and Navy SSR also happens annually.

Yes, apart from SSC, state police constable exams are held almost every year. Notifications differ by state but frequency is high.