Here are some nice materials for System Design for TECH roles
https://www.hiredintech.com/courses/system-design
https://www.hiredintech.com/classrooms/system-design/lesson/52
https://engineering.fb.com/
https://www.hiredintech.com/courses/system-design
https://www.hiredintech.com/classrooms/system-design/lesson/52
https://engineering.fb.com/