They have, they're the ones who decide to accept or not a studio offer based on what they want or if they want something specific they go themselves looking for a studio and companies, i feel like i posted this 3 times in the forum but again:
https://www.animenewsnetwork.com/in...-jump-editor-in-chief-hiroyuki-nakano/.143096
In the topics about animes Nakano basically says that SJ accept or denies the studio offers based on what they think is more suitable for the series, for BNHA and Neverland they were approached by the studios and accepted the seasonal format, Neverland being a case of a dark series and they needed detailed art and for that it would take time.
With Black Clover Nakano said that they wanted to be in a evening spot like Naruto and they also wanted to be produced for over a year so they picked Pierrot.
So basically they have a lot of say in the sense of being the ones who say the yes or no to the studios based on what they want for the series