Taking a wild guess, that sounds like a user browser setting, rather than a website setting.
Ctrl+Left Click - Open a link in a background tab.
Shift+Left Click - Open a link in a new browser window.https://www.howtogeek.com/114518/47-keyboard-shortcuts-that-work-in-all-web-browsers/
I'm not sure how you'd do that for "previous pages" unless you were viewing your browsing history.
Can you explain what you mean by, "open previous pages in separate tabs."