Bitstamp will show all prices in your local time zone and I believe there’s no option to change the timezone.
Since you are -6 hours of CET so you should check the price of BTC at Jun 20, 2021 18:00 (06:00 PM) to match with Jun 21, 2021 00:00.
ahh ok - that is what I was trying to determine if it calculated it based on where it thinks I am. I still don't see the same price as the one posted above.
Regardless, I am more than 10k from being right lol and Paxmao is still the closest either way.