Control-click a bookmark, then choose Open in New Tab from the shortcut menu.
Control-click a bookmarks folder, then choose Open in New Tabs.
Each bookmark in the folder opens in a new tab.
To open the bookmarks sidebar, click the Sidebar button on your Mac, choose Safari > Settings, then click Tabs.
Click the “Open pages in tabs instead of windows” pop-up menu, then choose an option:
Never: Links designed to open in new windows open in new windows.
Automatically: Links designed to open in new windows open in new tabs.
Always: All links designed to open in new windows open in new tabs, including links designed to open in specially formatted separate windows.
In the Safari app Close tabs in Safari on Mac