I applied online. The process took 4 weeks. I interviewed at Optiver
Interview
First there was an online assessment to test mathematical aptitude. After this, there is a phone screening. Then there were technical questions (stats/probability and game theory) over the phone and HR questions over zoom.
I have been able to do only the first part... neamely the part in which they ask to compute multiplication, division, addition, subtraction etcc. , it was though, But I think that if you prepare very well there are chances to go to the next step