If you arrive early at the AMS airport, you can get an antigen test in the airport. See this link: https://test2fly.com/
My wife flew back to the states a couple of weeks ago and as she was checking in at her US-bound flight, a passenger next to her had NO TEST. He was directed to the test2fly station and I later saw him heading BACK to the check-in counter - with a negative test doc in his hand - as I was heading for the parking lot. Thus, if you can't get a test conveniently elsewhere, you can get one at the Schiphol airport.
NOTE: There are apparently some restrictions on the "free test" option:
Holidaymakers will be able to make use of the free test by asking for
test compensation via a travel company or booking a test by a company
contracted by the Government, SchengenVisaInfo.com reports.