Not everyone gets the banner. U have to be eligible, and they determine who's eligible. If u dobt see it, then for some reason you arent. I'm not either, I went looking for it also
To my current understanding the beta is only available for note 10 and s10. It hasn't been released for any other phone yet, and trust me so far they haven't really changed much from Android 9. The most noticeable change it's the gesture control and the navigation bar, other than that it's really similar. Also the beta program for those that said they were not able to join is limited, they only had so many spots and they are all filled by now.
Only random people get the banner. But everyone on the Note9 should be able to upgrade to ths official One UI 2.0 update by January. S10 users will get it during December (probably).