The tabs are a system feature and work the same as tabs in other Mac apps. You can drag off a tab to a new window, or drag a tab between windows, or into another. You have to drag the tab, not the window itself - same a Safari or other tabbed window apps.
You can script tabs if you have specific needs to incorporate in an action: Docs
Is there a way to create a new tab using shortcut keys? If not, could that be added? CMD-T is already in use. Possibly SHIFT-CMD-N? I don’t think that is used.
I love love love that I can use tabs now but it’s a little bit cumbersome to create the new draft (which comes in on top of whatever draft I have open), then right click on it and say ‘Open in new tab’, and then go back to the old tab and hit the < (back) arrow to get back to my original draft.