The Czech Republic has opened up to Americans for tourist purposes. No need to quarantine or test on arrival. It seems as if you don't even need proof of vaccination or prior testing but please feel free to confirm or correct what I wrote.
This is for Americans coming directly from the USA or from another "green" country.
https://reopen.europa.eu/en/map/CZE/7001
(you have to do some searching to find the information)