So I spent an absolute age trying to add profiles to my S21 FE.
It turns out that this feature is not enabled on newer Samsung devices (well at least mine) even though it's available on Stock android.
I have requested this to be added separately but just wanted to get a feel for how many people would use it.
There's various reasons why I need to let family members sign in on my device and not use my account.
I'm just a bit surprised the option isn't there, I have an old Galaxy S tab and can have multiple user profiles on that.