💚The Buddha went straight to Buddhahood without becoming a non-returner?

💚If you're a non-returner and you go to the Brahma realms, then that is the only way to attain Nibbana in the Brahma realms? Is it possible to attain Buddhahood in the Bramha realms? Did the Buddha ever pass through the stage of non-returner or did he just jump straight to Buddhahood? An Arahant cannot become a Buddha? Aren't the 4 stages to enlightenment about mastering certain insights that one goes through momentarily? He was the Buddha when he taught the Abhidhamma from Heaven?