One UI 2.0 beta program has been live for Samsung Galaxy S9/S9 Plus devices in South Korea and also in India. So One UI Beta 2.0 or Android 10 should also be live in US soon for Samsung Unlocked S9/S9 Plus devices. One UI 2.0 Beta Program for S9/S9 Plus has been out a week after Note 9 got the beta program in South korea, so should be same time frame for the S9/S9+ in US too, after Note 9 devices gets beta updates. So just keep checking Samsung Members app for more information and for registration button, inorder to join beta program.
Yes that right, some of the features won't be working in Beta if you install beta updates. Beta updates is usually mostly for testing and finding bugs and letting Samsung know of issues and problems, so that final updates has no issues. Hope that things get better this year.