My interview loop was mostly UI related. All of these trading firms and hedge funds require UI expertise at some form, either for WPF/QT apps or web UXs for reactive charts, tables, etc.

Wow that nices so It's easy land a postion with these expertise too but I guess it hard to get your recognized in the first place

The loops were imho, pretty tough but focused on library specific knowledge while implementing algorithms in the form of live coding.