I'm not american but afaik it's very common. The US is on a different level though, see the flags in the suburbia, the pledge of allegiance in school's every morning etc.

But I'd say it's not "too much nationalism" rather the average american is defintiely more patriotic than an average european (who can then again be anyone from the UK to Poland to Moldova) but you get my point

I am American who has lived in many countries around the world, and I think this is distinctly wrong and the source of many problems in the US.

It would be more correct to say that the average American values outward displays of nationalism more, and has a more negative perception of those who do not appreciate or want to participate in those displays than people in most other countries. And yes, they conflate this with 'patriotism'. However, this is almost completely performative and lacks real substance, as is proven by the typically far more selfish attitude towards their fellow citizens, and is exemplified by the constant historical failures to provide significant funding for projects designed to help rather than harm others.

Europeans and people from other countries around the world are often fiercely in love with their countries. They just tend not to love the idea of noisily jumping up to gaudily beat their own drum. So yes, the average American thinks they are more nationalistic, when in fact they are just more tribal and crude about their nationalism than what is typically found in other countries around the world. If only our nationalism were taken a bit more seriously than our affiliation with a sports team, which is in theory just for fun and entertainment, that would be an improvement.

When I was younger, I would have thought that, but now I have trouble distinguishing nationalism and white supremacism when I see enthusiastic usage of flags/pledges.

Patriotism is soft nationalism, and any of either is too much.