@Maya ******
Depending on the direction the wind blows, all countries will probably fully reopen, but it will take some time. It's not going to happen in one fell swoop. I wouldn't even call Cambodia's announcement as a "full reopening" because it comes with conditions. It's probably as close to being "open" as you've been able to call it, since March 2020 though.
Vietnam has already said the final stage of reopening, meaning full unrestricted access by land, sea and air (meaning from borders with China, Laos and Cambodia) as well as cruises and regular, commercial flights, won't happen until June 2022.
Expect other countries to follow a similar schedule. Anything before June 2022 will only be a partial reopening or come with certain conditions.