Default Membership Option in Wordpress doesn´t exist

I am not able to enable user registration on my wordpress site? Normally it should be possible in Wordpress -> Setting -> General -> Memberships and then i have the option to decide which roles the new users get (Subscriber, Uthor, etc....) Why is this not possible right now?




Plugins i have: Elementor Pro, JetEngine.
Host: Siteground
I have Multisite installed: Here are the Network Settings:



But i cannot enable user registration and define roles.... WHy not?
Can you please help me, thanks in advance!