Strange. I'm using it on Emacs 30.0.90 (nightly builds), and haven't had that issue.
Personally I don't use its main menu though (which C-c , , runs), but rather "M-x howm-create" to capture new notes and then afterwards "M-x howm-list-all" as a keyboard-driven interface to read/browse/search existing notes.
Perhaps those commands work even if that menu doesn't?
I'm trying howm on emacs 29.4
I try (with my config and also with emacs -Q)
I enter `C-c , ,` I see the howm-memu pop up, but it's all plaintext with no font highlighting/decoration/"links" or anything, and I get in the Messages log: Is this familiar to anyone?