Under the hood, the league/commonmark package is used to render markdown. In the commonmark_options key of the markdown config file, you can pass any of the options mentioned in the league/commonmark docs.
If you want to pass options to be used by a particular instance of x-markdown, you can pass options to the options attribute.
<x-markdown :options="['commonmark' => ['enable_strong' => false]]">
# My title
</x-markdown>