Formats vary by company:
Google: min, whiteboard or virtual. Emphasis on scale and distributed systems. May pivot to discuss alternative approaches.
Meta: min, focus on product sense. "Design Facebook feature X." Expect to discuss metrics and success criteria.
Amazon: min, leadership principles woven in. "Tell me about a time..." mixed with design.
Microsoft: - min, often collaborative. May have interviewers.
Startups: Variable. Sometimes take-home, sometimes live. May use real codebase.
Preparation: Ask your recruiter about format. Different formats need different practice.