Well I'm not sure.
My source didn't say Sasuke created his Rasengan, he said they aided Boruto in creating a Rasengan.
So they probably gave him his chakra? Not clear.
He apparently uses Raiton (solely raiton) in the tournament. While he only knows how to channel it into his Rasengan in the movie.
He was pressured into using it by two people; The scientist, and his father (Naruto didn't realize he was pressuring his son tho)