Viet Cong in 1974 versus 2023?
You can’t make any sort of reasonable comparison. In 1974, the Cong were under strong communist rule and were fighting for their territory, which of course the regained.
Vietnam today is a communist country, but has moved strongly to become industrial / manufacturing and no longer agricultural. The Cong from 1974 are all in their 60s and 70s, and there is not a significant military today.
So if you’re asking – how would the 2023 US Army do against the 1974 Viet Cong? – the answer is ‘better than it did’ but still would take losses.
If you’re asking – how would the 2023 US army do against the 2023 Vietnam army – the US would win in a rout.