the space bar is occupied by the feature of getting total item in the view

I'm not sure what you mean by this. The number of items in the view just shows in the right-hand pane when nothing it selected in the items list.

This is a standard keyboard navigation feature of the list interface like the one in Zotero. Spacebar allows you to select and deselect items for multiple-item selection (along with Ctrl/Cmd-ArrowUp/ArrowDown to move the focused item). What is quicklook?

Yeah, that counter doesn't have anything to do with pressing the space bar. That just shows in the right-hand pane when no items are selected, including when you first click on a different library or collection. And you can always deselect the selected item with Cmd/Ctrl-click.

I don't know whether there's a QuickLook plugin that works in Zotero 7, but that's totally unrelated to this.

@dstillman, @adomasven, I have achieved the goal that type space bar for QuickLook, refer to: https://github.com/windingwind/zotero-actions-tags/discussions/132#discussioncomment-8904275