Cambodia will be one of the first places to reopen in SE Asia. I live in Siem Reap and it's been pretty much life as normal for the past 2 years. They are doing a great job vaccinated people and containing any outbreaks here.
Tourist's visas could be coming this month or November.
Where are you planning on staying? I would advise avoiding Siem Reap until next year. The entire city is under road construction. It's still OK here but the construction makes life a little more difficult.