Discussing sole author vs first authorship in ML/CV with supervisor
Just go with co-authorship
You're an undergraduate researcher.  This is a case where having co-authorship is actually better than sole authorship.  You said yourself it isn't groundbreaking.  By doing co-authorship you've created a google trail back to this professor.
When people are googling the professor's name, your paper will come up.  When people google your name, they will see your research network back to the professor.
Ph.D. students in the group likely talk about first/sole authorship more.
That's because Ph.D. students are expected to do high-level research and come up with novel ideas.  The next step in their career is (maybe) being a professor.
The next step in your career is getting into grad-school
The prestige of the professor your working with is a factor in admissions.  He'll probably write a recommendation anyway, but drive it home to admissions committees with a co-authorship.
From your post it sounds like he's pretty hands-off.  Write up the paper and put your name first and the profs second.  Let him tell you to swap them.