Arpit Bhayani is a US-based software engineer (formerly at Amazon, Practo, and now an independent educator) who runs asliengineering.com and the Arpit Bhayani YouTube channel, both focused on system design and database internals. His material is unusually deep for the system-design-interview market — taking serious detours into the actual implementation of Redis, Postgres, and the data structures behind them.
His CourseFlix listing carries three Arpit Bhayani courses: The System Design Masterclass, Redis Internals (an end-to-end study of how Redis is implemented in C), and System Design for Beginners. Material is paid and aimed at engineers preparing for system-design interviews or doing infrastructure work on production data systems.