I highly recommend working through https://dataintensive.net/ https://dataintensive.net/ with a pencil to make notes. It has enough information to get you throu

I highly recommend working through https://dataintensive.net/ https://dataintensive.net/ with a pencil to make notes. It has enough information to get you through basically any system design interview at a high level. After that you want to pick a tool for each category to learn in a bit more detail and screw around with if you think the interviewers might ask for details on your specific chosen technologies. Potentially learning the basic pros and cons would be enough. If you're going for more entry to mid level you likely won't need to get into the weeds of postgres index efficency etc in the interview. Designing Data Intenstive systems will get you about 80-90% of the way there though (in the UK), certainly enough to get through the door as a mid engineer in many bigger places, although possibly not a FAANG.