Hi,
I am running GNU emacs 27 (changeset "42ba6200af10c00c72ac13912d6fb42a7af88058")
and org-mime Version: 0.1.6, from melpa (Package-Version: 20190805.57)
seems to be the most recent one.

However please consider the following two equations inserted into a mail buffer and exported via
org-mime-htmlize
having org-mime-export-options is a variable defined in ‘org-mime.el’.
Its value is (:with-latex dvipng)
``
\begin{displaymath}
\int dx
\end{displaymath}

\begin{equation*}
\sum
\end{equation*}
''
that looks like a bug