As of today--of course things keep changing,
In total, of the 27 EU and 3 Schengen-area countries plus England on this list (31 in total) at present:

• 2 countries are closed entirely to U.S. travelers (Bulgaria and Norway).
• 2 countries are closed to unvaccinated U.S. travelers but open to vaccinated ones–Finland and Malta.
• 9 countries have quarantine requirements for unvaccinated American travelers (the Czech Republic, Estonia, Germany, Iceland, Ireland, Italy, Romania, Slovakia, and England).
• 29 countries are open to U.S. vaccinated travelers.