The interview was an initial casual interview and presentation, its was average and nothing out of the ordinary.
The problem was the absolute lack of feedback, neither positive nor negative, despite my follow-up email.
This is quite frustrating and, frankly, very unprofessional, particularly when the candidate has dedicated 4–5 hours of work.
As advice, the way you treat candidates is a proxy for your work culture, if there is a decent amount of poor feedback from candidates, I am inclined to think that this culture is also prevalent once you join, particularly when only 55% of employees and former employees approve of the CEO.