Ask HN: Non scam / web-course information on buying online ads for side business

I've recently started a few side projects (non technical) that have started to gain traction. However, both have stopped growing after a handful of word of mouth marketing got them noticed.

I've been meaning to start buying ads on Instagram and AdWords, however all of the available resources seem to be online course scammers (Garry V and the like) or are so surface level they don't seem useful.

If anyone has a blog or other in-depth resource for growth marketing / just how to intelligently buy online ads I'd really appreciate your input. And yes, I do realize there's an entire industry that dedicated itself to finding ways to do this for companies of all kinds.