The Galaxy S9 and Galaxy S9+ are now receiving the fourth Android 10 beta update. The newest beta, with build number G960FXXU7ZSLC and G965FXXU7ZSLC for the S9 and S9+ respectively, is rolling out in India and the UK at the time of this writing. It's a 139 MB download that includes plenty of bug fixes, considerably more than the number of fixes that were introduced in the previous beta that was released a week ago.
That doesn't mean Samsung has a lot of work left to do before it can release the stable Android 10 update for the Galaxy S9 and S9+. The final Android 10 beta for the Galaxy S10 series had a long list of bug fixes as well, but that didn't stop Samsung from pushing out the stable update to its 2019 flagship just a couple of days later. The same could happen in the case of the Galaxy S9/S9+ (and the Galaxy Note 9), though it probably won't be before January that the stable update makes an appearance.
To download the latest Android 10 beta for your Galaxy S9 or S9+, tap the Download and install option in the Software update menu of your phone's Settings app.
Update: Samsung has just released a hotfix update for the fourth Android 10 beta release for the Galaxy S9/S9+. The new update weighs 113 MB and includes fixes for the AOD time error and camera entry speed.