Since none of the answers (like this) did not work for me, please, take a look on following. In my document I have this (short example for clearance)
\usepackage[
backend=biber
,style=iso-numeric
,sortlocale=cs_CZ
,bibencoding=UTF8
]{biblatex}
\bibliography{file}
\begin{document}
\cite{some item}
\printblibliography
\end{document}
And I would like to typset surnames with small caps. Suggested use of
\renewcommand*{\mkbibnamefamily}[1]{\textsc{#1}}
\renewcommand*{\mkbibnameprefix}[1]{\textsc{#1}}
before \printblibliography is not working. What is wrong?

\lastnameformatis now\familynameformat(in line with https://tex.stackexchange.com/q/299036/35864). – moewe Jul 13 '20 at 16:09