I did not think I would stumble upon a theme that still uses Bootstrap in 2025 but... Here we are.

Bootstrap has kind of a CSS reset styling that makes dialog element display:block "by default." As a result, your dialog when closed looks like that:

A quick fix for such occasions would simply be re-adding your own "default" state to be dialog not opened: display none.

dialog#scm-dialog:not([open]) {
    display: none;
}

I know it's silly, because in this situation it's Bootstrap's fault and not your plugin's, but... it's hard to beat an outdated giant...