If you're in Bangkok, with Myanmar still closed, the closest is Aranyaprathet/Poi Phet. There used to be a minimum overnight stay in Cambodia, not sure if it's still in force. The Cambodians like foreigners to spend a night there to get ripped off and help the local economy 🤣.
I only mentioned it for the benefit of Australians, as the Sydney consulate is the only place where you can get the OX without transferring money to Thailand. If you're not Australian, don't even bother about it