It’s there for me on a Fairphone 3 running /e/OS S (Android 12) and on a Fairphone 2 running /e/OS R (Android 11).
Are you on an older Android version perhaps, where Seedvault wasn’t visible yet? … [HOWTO] Give complete /e/OS version info easily for support, answers, comparison etc
Else … if you’re looking for the term “backup” specifically, the term gets translated into the system language, so perhaps it’s not “backup” (in German for example it’s “Sicherung”).