documentclass{article}

usepackage{luatex85}
usepackage{fourier}
usepackage{fontspec}

setmainfont{Erewhon}[
    Extension=.otf,
    UprightFont=*-Regular,
    ItalicFont=*-Italic,
    BoldFont=*-Bold,
    BoldItalicFont=*-BoldItalic,
    SlantedFont=*-RegularSlanted,
    BoldSlantedFont=*-BoldSlanted,
    ]

setsansfont{texgyreheros}[
    Scale=MatchUppercase,% or MatchLowercase
    Extension=.otf,
    UprightFont=*-regular,
    ItalicFont=*-italic,
    BoldFont=*-bold,
    BoldItalicFont=*-bolditalic,
    ]

usepackage{bm,siunitx}

sisetup{
    unit-mode = text,
    locale=FR,
    detect-all,% Problème avec euro, utiliser text{€} en mode math
    inter-unit-product = ensuremath{{}cdot{}},
    group-minimum-digits=4,
    text-angstrom={Å},math-angstrom={text{Å}},
    text-micro=ensuremath{othermu},
    math-micro=othermu,
    detect-inline-weight = math
}

begin{document}
$num{5} SI{50}{km}$

$bm{bob{num{5}num{.1}SI{30}{km}}}$

 $num{0}<num{.03}<num{.045}<num{.09}<bm{{num{.1}}}$

textbf{SI{30}{km}}
end{document}