How can I find out whether an HDRI is normalized or not and how do I have to choose the settings for non-normalized HDRIs?
Pretty much all HDRIs are normalized since it's part of how they are made, so they'd have to be converted by someone on purpose. The only ones I know of are from Fabien and he explains them more here: https://www.youtube.com/watch?v=yrjWbdnTm7g