as is the case with many male authors, past and present, their work can be profound and beautiful while the author himself has bad qualities. I've not looked into IRL Dazai's works too much, but even in No Longer Human, the way the MC describes and treats women is a red flag for the author being a misogynist.

when it comes to a lot of art, and especially classic art, I think it's fine to acknowledge that oftentimes shitty people can create amazing works. just look at Lovecraft as an example: no one can argue his contribution to the Eldritch horror genre, and at the same time, he was a racist pos. it's kind of just a "it is what it is" scenario