We planned a trip flying to Paris from US on September 24 and then train to Amsterdam on September 24. Would we still have to quarantine in Amsterdam? Wondering if we should cancel trip.
From the Netherlands official site: https://www.government.nl/topics/coronavirus-covid-19/news/2021/09/03/changes-regarding-high-risk-and-very-high-risk-areas
So yes, you would have to quarantine. Transiting through another country won't exempt you.