The LaTeX macro \fillintext defined in pretext/xsl/pretext-latex.xsl has a dependency on the \real macro that comes from the LaTeX package calc. This package must be a dependency of at least one of the conditional packages that are loaded because the macro sometimes is defined and sometimes not. See the pretext-support discussion here: https://groups.google.com/g/pretext-support/c/jUxiSXdDjEU

I think the correction is to add a line to \usepackage{calc} to the standard LaTeX preamble. Is there a reason this should be conditional? The possibly related line \usetikzlibrary{calc} is always included, so I'm guessing the above package should as well.