Steps to Reproduce:
It would be really nice if I could drag the markdown preview to a new window so I can edit the markdown on one monitor and see the preview result on another monitor.
Also anything that uses the vscode.previewHtml command.
Right now the only options are to open on a side-panel or as a new tab that, as pointed out by @lovettchris, cannot be manually dragged to a new window.
This issue is related with #10121 which has many upvotes.
Hi @lovettchris also use two monitors to edit Markdown files with VSCode, as workaround I expand the window across all monitors like this:

This way I can edit my markdown files in one monitor and see rendered changes in the other :sweat_smile:
A workaround for me now it's use [Markdown Viewer]. Autoreload is include.
Another workaround:
use VSCode in the Cloud with code-server and let the browser take care of dragging the tabs around!
Most helpful comment
A workaround for me now it's use [Markdown Viewer]. Autoreload is include.