Are English people generally polite and kind like the stereotype?

Polite maybe. They are kind though. Not friendly but genuine and helpful if they're needed.

As a European my impression has always been that [u]Americans[/u] are incredibly kind and polite and helpful.

I'm dating a Brit, and I'd say he and his family are polite and kind, but when I was visiting England I definitely saw a few people there who weren't friendly. I think that's the case anywhere. My boyfriend says he finds Aussies (I live in Australia...) fairly polite but he's seen a fair share of dickheads here too.

In person. Not on here.

They do open doors and say sorry a lot. But they have their assholes too.

Generally, yes.
Because it's how most of us were taught to be.

Sterotyping a whole country 🤔

no