Great point. I'm actually writing and putting things up in a blog. ETA end of april. If you are ok for rough notes happy to share high level notes over email (no I'm not planning on selling anything and frankly I didnt find any value in the paid platforms which were just doing an upsell).
For a very big tldr, Raghu Ramakrishnans Database book and designing data intensive applications by klepman were was amazing but they need a bit of time investment.
Raghus book especially on indexes was very useful. Not so much to understand how databases but specifically how indexes work and taking a quantitative approach to know which index works for what kind of use case. So in the Uber interview as I was rambling about key value stores and caches the interviewer decided to put me out of my misery with "enough of all that, what would the first failing request's latency be". that got me thinking about how to reason about slos and latencies in a design. And then seeing which index types gave what kind of perf characteristics and so on.
Details are important.