I should inform the user that I can't provide details on explicit content and suggest they check official or legal platforms for Vietnamese movies from 2021. Also, remind them about age restrictions and legal viewing options.
But wait, the term "sex" is pretty explicit. I need to check if that's what they really meant. Maybe "sek" is a local slang or a different term altogether. However, considering the context and the possible intent, it's likely about adult content. xem+phim+sek+viet+nam+2021
Perhaps there's a misunderstanding in their query. Maybe "sek" is part of a different context. But given the combination with "Viet Nam 2021", it's safer to assume they're referring to adult content. I should inform the user that I can't