Resources for Gen AI / System Design?

Hi guys! After multiple interviews across startups that establish the fact that forward deployed AI engineers and System Design enthusiasts are on the rise, I am feeling lost. I wanted to start off fresh with a solid perspective onto 2026, and was wondering which resource works best to combine the two concepts? Every time I do interviews with LLM models to see where I stand, I always find myself lacking. Say for example - How to handle 10 mil docs while ensuring 1 minute “freshness” SLA? This can have multiple answers.