\documentclass{article}

\renewcommand\bfdefault{sb}
\usepackage{plex-serif}
\renewcommand\bfdefault{sb}

\begin{document}

\Huge\noindent
\fontseries{b}\selectfont and \\
\textbf{and} \\
\fontseries{sb}\selectfont and


\end{document}