What are the most reliable SEO courses you go back to when trying to remember topics you need to recall?

I'm a financial manager with a year of experience in Digital marketing and want to venture into SEO as a side hustle. I dreamt of starting a website of my own and start selling products, basically to move out of my 8 to 5 job. I have a bit of experience in developing websites and product branding and want to know if there are credible sources you can recommend for newbies to look into.

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<may attract promoters of courses but if it's okay, at least state your experience to add credibility with your suggestions? 😬>