It doesn't work for me. Even after I've deleted all os2world cookies, the browser keeps me logged in on the main site
https://www.os2world.com/cms/ only until I close all browser windows.
On opening the main site, the first cookie in the screenshot is created. It's a session cookie, that's deleted after a browser session.
The second joomla_remember_me_* cookie is added after I log in. It expires after a month. I guess that's the one that doesn't do what it should.
The third and fourth cookies are created after I've opened this thread. These are SMF pages. The PHPSESSID cookie expires at the end of the session and the SMFCookie* is the one that successfully keeps me logged in on the SMF pages until 2026.