The Preview button and associated functionality is currently undergoing a fair amount of iteration – I would imagine we will see a keyboard shortcut added, along with other options for modifying it’s UI down the road.
A Big Hack
Interestingly, the old direct-preview button’s component is still rendered, but is hidden on a > 600px media query. We can reveal the button again with a little CSS:
.edit-post-header__settings .editor-post-preview {
display: block;
}
I wouldn’t rely on this working indefinitely, however.
A Little Hack
For now, the most canonical solution would probably be to register a block editor plugin which renders a new <PostPreviewButton>
component as a child of a <PinnedItems>
slotfill.
It should be noted that doing this directly undermines the UX design for the
<PinnedItems>
slotfill and area, which is intended to show buttons for functionality which the user explicitly opts in to. Thus, were this to be distributed in a plugin, it would be a good idea to associate it with a toggleable editor setting.