Actually SEO fundementals is not so hard to understand. You can find thousands of sources and on the most of them will be the same things.
And then when you actually will understand how search engines works, and what factors have value, or maybe potential can have value for Google and others engines. You will have a lot of questions, like "How to increase your website trust", "How to make optimized SEO articles", "What keywords to use", "How to rise your conversion", "What link are good for your website, or what links harming your site", "How to work with analyze your website or niche" and so on and so on... Finding answers to these questions, you will gradually become a SEO expert.
And I think the main rule, is that SEO is all about action, not bulshit theory. You need to test all those theories and ideas.
Even the greatest articles from MoZ blog or Backlinko may give some ideas or interesting cases, but all this stuff without real practise, can help you only to rewrite another SEO article "how to learn SEO" or something like this. Is not so hard or expensive to create a website (on Wordpress or other CMS) in our days. So create a site for the start not in a to much competitive niche and just hustle...