In the answer to this thread it is advised to use the package xparse released 05/03/2019 or later. I've been trying to update this specific package, but without success.
First I updated all the packages with the command
tlmgr update --all
hoping that this would automatically install the latest version of xparse (which is in the l3packages bundle). Unfortunately that didn't happen, since compiling the code
\documentclass{article}
\usepackage{xparse}
\listfiles
\begin{document}
\end{document}
the log file shows that I'm using the xparse version released on 2018-10-17.
How can I force the update?

xparseon your current frozen TeX live 2018, you need to install the package manually, see https://tex.stackexchange.com/q/117518/35864 and https://tex.stackexchange.com/q/73016/35864. (I would not recommend that.) – moewe Apr 28 '19 at 15:42xparseyou probably also need to update all otherexpl3kernel packages. – moewe Apr 28 '19 at 15:43xparseis not in TeX live 2018) and then it needs a bit of time to ready the next release. In this case roughly until 2019-04-30. There is no officially advertised simple way to update TeX live 2018 to TeX live 2019. You just install TeX live 2019 (you don't have to uninstall TeX live 2018, the versions can coexist). See also https://tex.stackexchange.com/q/107017/35864 (apparently there are ways to upgrade, but they are not tested much...) – moewe Apr 28 '19 at 16:32