My original post had me mistyping fcitx5-mozc where I meant fcitx5-anthy. I've fixed it, but no, there isn't, as of March 9, 2024, a ja-fcitx5-mozc, only anthy. So, I've fixed this post, but T-Aoki was correct, my original said fcitx5-mozc.
Well, had to do a reinstall on my main workstation...