The plant in the photos is Ophiopogon reversus C.C. Huang described from Hainan, China.
I am glad to know that this was newly found in Vietnam (new record!).
Record creation: 2021-11-12, Leonid Averyanov, PhotoScan D2Citation: Specimen LE 01122998 // Virtual herbarium of Komarov Botanical Institute RAS — http://re.herbariumle.ru/01122998