Blackboard does not have method to add a caption to an inline image and the Content Styler does not have a way to determine what is a caption for an inline image (it just gets too messy).

By editing the HTML directly a caption can be added to an inline figure by wrapping the IMG element in a FIGURE element and adding a FIGCAPTION element.

<figure class="figure">
    <img class="figure-img img-fluid rounded" src="...image url..." alt="...accessibility description...">
    <figcaption class="figure-caption text-end">...caption text...</figcaption>
</figure>