Samsung did not confirm when, but it is very likely support for other countries will land soon. That would include China, Germany, India, South Korea, and the United States.
Meanwhile, news spread earlier today that One UI 4 beta support was also rolling out to the Galaxy S20 series (also via SamMobile). However, Samsung pulled this update for now. That didn’t stop some folks from being able to register for it here in the US, but a full rollout will likely come soon.
Either way, to get access to Android 12 on your Samsung device, you’ll need the Samsung Members app. Log in to that app with your Samsung account and then search for the One UI beta banner. If you don’t see it, the beta isn’t available for you yet, but keep checking to nab your slot as soon as you can.