textlangle and textrangle, with kpfonts-otf, not displayed with lualatex but displayed with xelatex

The luatex log shows

Missing character: There is no 〈 (U+2329) in font [KpRoman-Regular.otf]:mode=n

It works in luatex if you use HarfBuzz (like xetex)

documentclass{article}
usepackage{iftex}
ifpdftex
usepackage[T1]{fontenc}
usepackage{kpfonts}
else
usepackage{fontspec}
ifluatex
defaultfontfeatures{Renderer=HarfBuzz}
fi
usepackage{kpfonts-otf}
fi
begin{document}

verb|$langlerangle$| $=langlerangle$

verb|textlangletextrangle| $=$ textlangletextrangle

end{document}

In theory (but apparently not in practice) U+2329 shouldn't be used, it has an unfortunate Unicode normalization to a full width angle bracket in the CJK block and U+27E8 was added specifically to avoid this character.

LaTeX's textlangle and textrangle insert Unicode codepoints U+2329 and U+232A by default. In your font, these glyphs do not exists, but Unicode codepoints U+3008 and U+3009 are available. According to Unicode data tables, these are canonically equivalent (meaning they "should" always appear exactly the same) to U+2329 and U+232A, so HarfBuzz (used by XeTeX and when explicitly requested by LuaTex) substitutes these. (This is a bit problematic because U+3008 and U+3009 are CJK characters and therefore might be wider in many fonts, but that's not an issue with kpfonts.)

To get the correct glyphs also in LuaTeX you can enable HarfBuzz or change which codepoints LaTeX uses:

documentclass{article}
usepackage{iftex}
ifpdftex
usepackage[T1]{fontenc}
usepackage{kpfonts}
else
usepackage{kpfonts-otf}
DeclareTextSymbol{textlangle}UnicodeEncodingName{"3008}
DeclareTextSymbol{textrangle}UnicodeEncodingName{"3009}
fi

begin{document}
verb|$langlerangle$| $=langlerangle$
verb|textlangletextrangle| $=$ textlangletextrangle
end{document}