If you often use MAC for work and default typing VNI or have a problem with 1 underline when typing and you have found many ways to fix it such as turning off spell check, turning off this and that but still can't.
The main reason is that MAC's default percussion is still not optimized and cares much for VN users.
The fix requires the use of third-party software, which is the Gotiengviet percussion author Tran Ky Nam (free). Download at this page https://www.trankynam.com/gotv/
After the installation is complete, now the percussion will be smooth as usual, in addition, the percussion will understand the Vietnamese people's mood better than evidence if you type telex, the percussion will support and understand in cases where you are close to typing the ending. Vietnamese brother.