Algoexpert

I am looking for good resources for system design. So far I have skimmed a couple of youtube channels, Algoexpert, highscalability, grokking the system design interview. I think I liked AlgoExpert the most. But I wish it had more system design interview questions. Most of the resources that I have come across, somehow feel shallow. I wish they added a bit more depth to it. There are always certain areas that are left too vague. Is there any other resource? Free or paid. As long as it is good.