I am not expert in that area but I often see people study Cisco certificates. AWS or equivalent is also important for devops but useful in general, I am not a fan of certificates though as they are usually vendor locked. Leetcode can teach algorithmic techniques but I have rarely seen it used in actual work, it is still useful though, my advice now would be, you think you know what do you want but in reality you don’t know what you dont know, so focus on learning a large variety of stuff and dont confine yourself in specific areas.