Searching for an indentation problem, I found this question How to add indentation and this answer https://tex.stackexchange.com/a/392800/77017.
In the comments @cfr identified this as a "not so good" answer, because it is lacking glue.
So here is my question: what is glue and why is glue important?
\vspace{6mm}and\hspace*{10mm}are examples of manually inserted glue.