The only influencer I can think of who's written fiction (excluding Zoella) is Joey Graceffa. Fiction is definitely not a common money spinner as I presume it's harder to promote.
I think the logic is that it's easier to promote in many ways, since publishers are selling to an existing audience/fanbase who will (in theory) buy any old
tit with the influencer's name on it. The influencer also has an established platform and social media base to promote from themselves, eliminating a lot of the publisher's marketing costs and responsibilities, versus the publisher having to do much more legwork themselves introducing a brand new, unknown author to the market.
It's definitely less of a thing than influencer non-fiction, but it still happens fairly prominently. Aside from Zoella, Carrie Hope Fletcher keeps getting things published. Booktubers like Christine Riccio and Sasha Alsberg got book deals that never would've happened without their existing social media brand.
The things they all have in common books is that the books were all completely terrible, even with the help of established author co-writers and uncredited ghostwriters.
What little I read of Christine Riccio's book was absolutely atrocious. It's filled with more shoe-horned pop-culture references than a dozen copies of Ready Player One. Babe Lozenge and Pilot Penn are actual names that she included for major characters, like she got stuck for ideas and started naming them after household objects.
Between her and Sasha Alsberg, they pretty much killed the market for booktuber fiction, since they were absolutely savaged critically and most people only bought them to experience the cringe.
I can't see Jack of all people being the one to break the trend. He'll either give up and lose interest after milking some money and content out of his "writing journey", or it'll be an unmitigated disaster of a book.