You can live here. Nobody is claiming otherwise. You can live here perfectly well.
But how do you live? Comfortably? Or is it work, then home, and repeat?
Especially for those working at Vietnamese companies
You speak Vietnamese all day. I am not criticising that, but I want more happiness for you than that.
Making local friends. Working with them, talking with them. Being able to talk about love, about life, about what motivates you, with people who live here.
Whereas if you are here but always on the phone to Vietnamese friends, always calling home, that is fine too. But it is very hard to widen your world that way. You do not connect deeply with anyone.
The practical number
For real connection, you genuinely need around 6.5.
At 5.5 you can handle the technical side of life: renting a flat, doing the paperwork, even running a small business.
But 5.5 makes deep connection very hard. They are two different things.
Why it is worth pushing further
A few more sentences, communicating a bit better, and you might open up business contacts, or actual friendships.
The gap between "surviving" and "living comfortably" is often only a band or two. But it is the gap between being in a place and belonging to it.