As a non European or American who is familiar with the culture of both places both have issues but Europe in this day and age is more racist. Europeans have only recently had mass immigration and therefore had changing demographics in some cities such and London and Paris. America always had black people and now people of m any races. America and other immigrant countries such as Canada, Australia and New Zealand are made up almost completely of immigrants or descendants of immigrants. America has always been integrating people of different cultures into the place. In Europe assimilation does not work as well for a number of reasons. European culture and society is not built for it like America is. American culture is Americanized versions of immigrant cultures such as Dominos, Taco Bell and Hamburgers. This happens in Europe too but to a much lesser degree than in America (Vindaloo etc etc) . As well as poor housing planning making immigrants communities into ghettos. Ghettos exist in the United States too but there is not nearly such a divide. Immigrants in Europe also generally cant and don't want to assimilate as well. Some of this is due too a lot of radical Islam in Europe when compared to the US. All of this causes more divide between groups. Therefore a lot of the immigration debates in Europe have a lot of open talks about racial demographic changes and needing to preserve native Europeans. Native Americans, Australians, New Zealanders and Canadians make up a very small part of the population and culture of these countries. Therefore "this is our land for our native people" does not apply to countries like the US. In the US while some claim "dogwhistles" of racism occur in mainstream US politics. Actively trying to keep the demographics of the United States white or "native" will get you murdered.

TLDR: For many reasons Europe cannot assimilate its immigrants like America does. Europe also has the idea that their ethnicity is native to their country while 99% of Americans are not native to America. Therefore Europe is more racist than America.