Hello vishal . There is no gap year between jee mains and jee advance Joint allocation authority only gives you a month or two may be due to this pandemic to prepare for jee advance and then you have to write the paper if you attempted jee mains and not jee advance so to apply jee advance next year you need to again qualify jee mains as you can understand it as a door to jee advance . Dont miss jee advance this year if you had applied for jee mains and already qualified .

Hope it helps