That's why internet is extremely slow here, I am in Myanmar
Myanmar is not directly connected to Vietnam via sea cables specifically. The major connections to the outside world via the sea are:
https://www.submarinecablemap.com/submarine-cable/seamewe-5
https://www.submarinecablemap.com/submarine-cable/asia-afric...
https://www.submarinecablemap.com/submarine-cable/seamewe-3
https://www.submarinecablemap.com/submarine-cable/singapore-...
Additionally the cable in question comes from Europe, so the Vietnam break shouldn’t affect Myanmar (which also has direct access to it) https://commons.wikimedia.org/wiki/File:SEA-ME-WE-3-Route.pn...