How to get started learning about SEO

Hi,

I'm working in online marketing, but I'm fairly new to SEO. I've worked with Wordpress before, done some keyword research on Ubersuggest and Ahrefs and I've optimized content. I really wanna learn a lot more about SEO, especially the technical side, like SEO tools, analytics, audits. Can anyone point me in the right direction? What's the best way to learn? Buy a udemy course? Watch Youtube videos? Anything else? Also, what would you recommend learning as a must-know?

Thanks!