The full version of Finereader Pro supports Vietnamese. Since I don’t speak the language, I can’t comment on its accuracy.
There is a Devonthink script that allows you to use an external copy of Finereader Pro. Among other things, it brings OCR to the non-pro version of DEVONthink.
I’m still using Mojave, though, and I have heard that both Catalina and Big Sur make this kind of inter-application scripting more difficult.