S.T. Joshi’s Liberation newspaper interview, in French: “Lovecraft admettait lui-meme que les relations humaines ne l’interessaient pas”. Now online and public, and with no paywall that I can see, but it may be one of those “the first view is free” newspapers.

Via Google Translate:

Q: Could you have written more with more [source] material, and are you planning a new version?

A: The biography is largely based on Lovecraft’s letters, an incredible source that often represents an almost daily chronicle of his life. This raw material does not interest everyone, and it needs to be interpreted to make it fit a coherent narrative frame. I could add more details to my biography, but it would not serve much purpose. Although in the last ten years we have learned new facts, and facts about Lovecraft. But I think I have already said a lot.